Abstract:
A composite train housing for pseudo-planetary kinematic transmission, which comprises three components namely two external ones fixed to a central one, axial posts being formed between the components.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a composite train housing for pseudo-planetary kinematic transmission. 
   Known coaxial kinematic transmissions that need to obtain ratios of more than 7-8 by using simple sun-and-planet gear systems generally entail the adoption of multiple reduction (or step-up) stages if trains of the type shown in  FIG. 1  of the accompanying drawings are adopted. 
   In  FIG. 1 , X 1  and X 2  designate the shafts between which motion is transmitted (speeds {overscore (ω)} 1  and {overscore (ω)} 2 ), A designates the sun gear, B designates the internal ring gear, a and b designate the planet gears, and the train housing is designated by U. 
   There are still good possibilities of execution, for average ratios which are in any case higher than those possible with the type shown in  FIG. 1 , when using trains of the type shown in  FIG. 2  (in which the same terms are used), in which the planet gears a and b are coupled, with the advantage of obtaining the required ratio with a single set instead of two trains of  FIG. 1  arranged in a cascade configuration. 
   Furthermore, in the case of  FIG. 2  a single internal ring gear is used, whereas it is difficult to manufacture planet gears a and b of very high precision as regards the phasing between the toothed bands, in order to ensure correct meshing with the mating gears. 
   If one wishes to use a sun-and-planet gear system in high-speed transmissions, it is currently necessary to keep the train housing or spider U motionless, in order to avoid centrifugal stresses on the planet gears a and b and especially on the bearings of the planet gears. 
   In the case of a fixed train housing or spider U and of rotating sun gear A and internal ring gear B, the reduction train is termed pseudo-planetary. 
   This is true both for the type shown in FIG.  1  and for the type shown in FIG.  2 . 
   A characteristic of this solution is the opposite direction of rotation between the input and the output. 
   A considerable limitation to the production of a pseudo-planetary train of the type shown in  FIG. 2  is constituted by the limited space available for providing a rigid structure for the train housing U, which is formed monolithically, with particular reference to the posts that connect the two shoulders of said train housing, as shown in particular in  FIGS. 3 and 4  (which are diametrical and transverse sectional views of a reduction unit), in which the posts are designated by M and the shoulders are designated by S. 
   This limitation is linked to the need to join the two shoulders S by passing close to both series of planet gears a and b and remaining within the addendum circle of the internal set of teeth B. 
   The result is a highly convoluted shape of the posts M that is almost always very narrow if not entirely insufficient. 
   The problem of the assembly of the various components is also very difficult and sometimes even impossible. 
   Moreover, it is impossible to adopt large bearings, whose presence would be sometimes desirable. 
   SUMMARY OF THE INVENTION 
   The aim of the present invention is to provide a train housing or spider for pseudo-planetary kinematic transmission that eliminates the drawbacks mentioned above in known types, combining high operating rigidity with easy assembly and high machining quality. 
   Within this aim, a primary object is to meet the possible need to adopt large bearings. 
   Another object is to have a high rigidity of the train housing body and to minimize vibrations and flexing of the structure under the most challenging load conditions. 
   Another object is to provide all of the above at a reasonable cost. 
   This aim and these and other objects that will become better apparent hereinafter are achieved by a train housing for pseudo-planetary kinematic transmission, characterized in that it is composite and comprises three components, namely two external ones fixed to a central one, axial posts being formed between said components. 
   Advantageously, each one of the two external components of said three is provided monolithically with its own axial post, directed toward said central element and fixed thereto. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further characteristics and advantages of the present invention will become better apparent from the following detailed description of an embodiment thereof, illustrated only by way of non-limitative example in the accompanying drawings, wherein: 
       FIG. 1  is a diagram of a first type of transmission according to the prior art; 
       FIG. 2  is a diagram of a second type of transmission according to the prior art; 
       FIGS. 3 and 4  are sectional views, taken along mutually perpendicular planes, of a transmission (reduction unit) according to the diagram of  FIG. 2 ; 
       FIG. 5  is a sectional view of a transmission (reduction unit) provided with a train housing according to the present invention; 
       FIG. 6  is an exploded perspective view of the train housing according to the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With reference to  FIGS. 5 and 6 , a speed reduction unit provided with a train housing or spider according to the present invention substantially comprises a sun gear  1 , an internal ring gear  2 , pairs of planet gears, each composed of planet gears  3  and  4  that are rigidly coupled to a common pivot  5  whose ends are rotatably coupled, by means of bearings  6  and  7 , to a fixed train housing  8 . 
   The train housing, according to the invention, is composite, i.e. has a composite structure or arrangement, and comprises two disk-like external components or elements, designated by the reference numerals  9  and  10  respectively, which monolithically and peripherally support its own axial post (protrusion), designated by the reference numerals  11  and  12  respectively, which are directed toward, and fixed to, a central element  13 , which is also disk-like. 
   The posts  11  and  12 , which are nothing other than elements for connecting one another the components of the train housing  8  in the regions engaged axially by the planet gears  3  and  4 , are conveniently arranged at the same angular positions, intercalated with those of the seats  19  and  20  of the bearings  6  and  7 . 
   The set is preassembled, by means of bolts  14  that pass through suitable through holes  15 ,  16 ,  17  and  18 , which pass through the elements  9 ,  10  and  13  and the posts  11  and  12  before the final machining of the seats  19  and  20  of the bearings  6  and  7  that support the planetary gears  3  and  4  and of the reference surfaces, so as to ensure maximum precision together with easy execution. 
   The element  9 , on the opposite side with respect to its posts  11 , is shaped so as to define a flange  21  for fixing to the body of the reduction unit (not shown in the figures) with the aid of an annular element  22  that is fixed to the flange  21  by means of bolts (not shown). 
   The three elements  9 ,  10  and  13  can be separated one another after machining and easily reassembled, so as to not be a problem for rapid and precise assembly of the various components of the kinematic chain. 
   In practice it has been observed that the intended aim and objects of the present invention have been achieved. 
   The new train housing  8  in fact has maximum dimensions with respect to the space available proximate to the rotating parts, with correct transfer of stresses and minimum impact on overall space occupation. 
   The limits set by the dimensions of the sets of teeth of the planet gears  3  and  4  and of the internal ring gear  2  are thus overcome, with ample possibilities of solutions to meet also the need to adopt large bearings (which, as mentioned in the preamble, could not be used before due to the limited space available). 
   Moreover, there is a high rigidity of the train housing body  8 , with great benefit in minimizing vibrations and flexing of the structure under the most demanding load conditions. 
   The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims. 
   In practice, the materials employed, so long as they are compatible with the contingent use, as well as the dimensions, may be any according to requirements. 
   The disclosures in Italian Patent Application No. PD2001A000123 from which this application claims priority are incorporated herein by reference.