Abstract:
An angular reducer with two or three reduction stages, wherein the casing is designed to selectively house two or three reduction stages, while maintaining unchanged, when switching from two to three stages or vice versa, the mutual positions of the axis of the drive shaft and the axis of the driven shaft; and wherein the casing has a number of inner supports for supporting the two alternative gear trains.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a multistage angular reducer. 
     As is known, reducers of the above type comprise a casing, an input drive shaft, an output driven shaft, and a number of reduction stages housed inside the casing and interposed between the drive and driven shafts. 
     The main drawback of currently marketed reducers lies in the casing being designed to house either two or three reduction stages, with no possibility of varying the number of stages in the casing by means of straightforward operations (e.g. switch from two to three stages or vice versa). That is, it is not possible to switch from a two-stage to a three-stage design using the same casing, which lacks the seats for supporting the mechanisms required for converting the gear train from one design to the other. The first stage of currently marketed motor reducers is nearly always defined by a bevel pinion meshing with a bevel ring gear, which means the stage producing the most vibration is located at the start of the gear train, thus increasing the noise level of the system as a whole. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a multistage angular reducer designed to overcome the aforementioned drawbacks. 
     According to the present invention, there is provided a multistage angular reducer of the type comprising: 
     a casing; 
     a drive shaft; 
     a driven shaft connected to a user element; and 
     a number of reduction stages housed inside the casing, between the drive shaft and the driven shaft; 
     wherein the casing is designed to selectively house two or three reduction stages, while maintaining unchanged, when switching from two to three stages or vice versa, the mutual positions of the axis of the drive shaft and the axis of the driven shaft; and wherein the casing comprises a number of inner supports for supporting the two alternative gear trains comprising a number of shafts and toothed elements. 
     Moreover, the stage comprising the bevel pinion is never located at the start of the gear train. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A number of preferred, non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which (elements performing the same or similar functions are indicated using the same numbering system): 
     FIG. 1 shows a preferred embodiment of a two-stage angular reducer in accordance with the present invention; 
     FIG. 2 shows a cross section of the preferred embodiment in FIG. 1; 
     FIG. 3 shows a preferred embodiment of a three-stage angular reducer in accordance with the present invention and featuring the same casing as the FIGS. 1 and 2 reducer; 
     FIG. 4 shows a section of the casing of the reducer in FIGS. 1 to 3; 
     FIG. 5 shows a first section of the FIG. 4. casing; 
     FIG. 6 shows a side view of the casing in the above drawings; 
     FIG. 7 shows a second section of the FIG. 4 casing and; 
     FIG. 8 shows a third section of the FIG. 4 casing. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the FIGS. 1 and 2 embodiment, the angular reducer 1 comprises two reduction stages 3, 4 housed inside a casing 2. The first stage 3 comprises a first cylindrical gear 32 (of axis K) integral with a drive shaft 31, and which meshes with a second cylindrical gear 5 fitted to a shaft 6 supported by two bearings 7, 8. 
     The second stage 4 in the FIGS. 1 and 2 embodiment comprises a hypoid bevel pinion 9 meshing with a bevel ring gear 10 integral with a driven shaft 11 (of axis M) (FIG. 2). 
     As shown in FIGS. 1 and 2, the hypoid pinion 9 is supported by the same shaft 6 to which the second cylindrical gear 5 is fitted, and which, as stated, is in turn supported by the bearings 7, 8, which are supported by inner supports 12, 13. 
     The Casing 2 comprises a number of walls 14-19 defining a box structure; wall 14 comprises an opening 20 through which motion is transmitted from the first cylindrical gear 32 to the second cylindrical gear 5; and seats 21, 22 (FIG. 2) are formed respectively in walls 18, 19 to support the driven shaft 11 by means of bearings 24, 25, and therefore also support the bevel ring gear 10 integral with the driven shaft 11. 
     In the FIGS. 1 and 2 embodiment featuring two stages 3, 4, shaft the 6 to which second cylindrical gear 5 is fitted also supports the hypoid pinion 9, which, as stated, meshes with the bevel ring gear 10 to transmit motion from the shaft 6 to driven shaft 11. As shown in FIG. 1, the inner supports 12, 13, and therefore also the respective bearings 7, 8, are located in the gap between the second cylindrical gear 5 and the hypoid bevel pinion 9. 
     In the two-stage reducer, motion &#34;enters&#34; the casing 2 via the first reduction stage 3 defined by the first cylindrical gear 32 meshing with the second cylindrical gear 5, &#34;passes&#34; through the second reduction stage 4 defined by the hypoid pinion 9 meshing with the bevel ring gear 10, and &#34;leaves&#34; from the driven shaft 11 which drives a user element (not shown). 
     To switch to a three-stage reducer 1 using the same casing 2 and maintaining the the same distance between axes K and M, a third stage 23 must be added. That is, a second pair of inner supports 24, 25 supporting a countershaft 28 by means of respective bearings 26, 27 must be provided. In the three-stage embodiment shown in FIG. 3, the shaft 6 of the FIG. 1 two-stage reducer is replaced by a toothed shaft 29 meshing with a third cylindrical gear 30 fitted to the countershaft 28, which also supports a bevel pinion 39. The third cylindrical gear 30 and the bevel pinion 39 are housed inside the gap defined by the inner supports 24 and 25, which, for the elements of the three-stage gear train to mesh properly, are offset with respect to the inner supports 12 and 13. 
     In a preferred embodiment of the invention, the four inner supports 12, 13, 24, 25 may be formed in one piece with the casing 2. 
     The inner supports 24, 25 are also obviously provided in the FIG. 1 embodiment featuring only the two reduction stages 3, 4, in which case, only inner supports 12 and 13 are used for supporting the transmission elements. 
     The third reduction stage 23 is located between the first stage 3 and the second stage 34, which is &#34;shifted&#34; so to speak to permit insertion of the third reduction stage 23. Though specific reference is made in the FIG. 3 embodiment to a toothed shaft 29, this may obviously be replaced by any equivalent transmission member (e.g. a cylindrical gear integral with a shaft resting on inner supports 12, 13). 
     As shown in the accompanying drawings, the axis of the inner supports 24, 25 is coplanar and perpendicular to axis M of the seats 21, 22, so as to define a plane not containing axis K of drive shaft 31. 
     FIGS. 4-8 show more clearly the mutual positions of the inner supports 12, 13, 24, 25, also with respect to the walls 14-19 defining the casing 2. 
     The reducer described therefore provides for considerable saving in terms of production and storage cost, by enabling the same casing to be used for two or three stages, as required by the user. Moreover, substitution of the gear train is a highly straightforward job not requiring the use of particularly skilled labour. 
     Clearly, changes may be made to the angular reducer as described and illustrated herein without, however, departing from the scope of the present invention.