Abstract:
A farm vehicle power take-off device, in particular for a tractor, wherein an output shaft is connected selectively by a drive to a first and second input shaft rotating at different speeds. The selective connection is made by moving a selector sleeve between three settings, in a first and second of which, the output shaft is connected to the first shaft to rotate at a first and second angular speed respectively, and, in a third of which, the output shaft is connected to the second shaft to rotate at a third angular speed different from the first and second angular speed.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a farm vehicle power take-off device, in particular for a tractor. 
       BACKGROUND OF THE INVENTION 
       [0002]    In typical power take-off devices the first shaft is an engine shaft, and the second shaft a shaft of the vehicle transmission, so that, when the output shaft is connected angularly by the drive to the second shaft, the angular speed, corresponding to the third speed, at the power take-off end is proportional to the angular speed of the shaft transmitting power to the vehicle wheels. For this reason, the third speed is commonly referred to as “ground speed”, and is advantageously used for transmitting power to the wheels of a trailer. 
         [0003]    In a power take-off device of the above type, selection is made, as described, for example, in US 2002/0043121, by means of two sleeves: a first sleeve is coaxial with the first shaft, and is movable axially between two work settings corresponding to the first and second speed respectively, and an intermediate idle setting corresponding to a neutral position of the output shaft; and a second sleeve is coaxial with the second shaft, and is movable axially between a work setting corresponding to the third speed, and an idle setting corresponding to a further neutral position of the output shaft. 
         [0004]    Each sleeve can only be set to the/a respective work setting when the other sleeve is idle, and both are user-operated by respective control levers located in the vehicle cab and connected to the respective sleeves by respective drives. 
         [0005]    Though effective and widely used, the above device has several drawbacks in production and operation relating to the mechanical complexity of the device. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention relates to a power take-off device of the type comprising an output shaft having a power take-off end connectable to a machine or trailer; and a drive interposed between the output shaft and a first and second input shaft rotating at different angular speeds; the drive comprising selection means for selectively connecting the output shaft to the first and second shaft, and being so designed that the output shaft, when connected to the first shaft, rotates at a first or second angular speed, in particular 750 (or 1000) rpm and 540 rpm, and, when connected to the second shaft, rotates at a third angular speed different from the first and second speed. 
         [0007]    It is an object of the invention to provide a power take-off device, which is cheap and easy to produce and, at the same time, easy to operate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: 
           [0009]      FIG. 1  shows a partial sectional view of a preferred embodiment of the power take-off device, with parts removed for clarity, according to the present invention; 
           [0010]      FIG. 2  shows a detail view of the power take-off device of  FIG. 1 , in a first operating positions; 
           [0011]      FIG. 3  shows a detail view of the power take-off device of  FIG. 1 , in a selection position correspondingly to an idle position of the stubs; 
           [0012]      FIG. 4  shows a detail view of the power take-off device of  FIG. 1 , with the sleeve in a second operating position; 
           [0013]      FIG. 5  shows a detail view of the power take-off device of  FIG. 1 , with the sleeve in a second selection position; 
           [0014]      FIG. 6  shows a detail view of the power take-off device of  FIG. 1 , with the sleeve in a third operating position; 
           [0015]      FIG. 7  shows a detail view of the power take-off device of  FIG. 2 , with the sleeve in a first operating position; 
           [0016]      FIG. 8  shows a detail view of the power take-off device of  FIG. 4 , with the sleeve in a second operating position; 
           [0017]      FIG. 9  shows a detail view of the power take-off device of  FIG. 6 , with the sleeve in a third operating position; 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0018]      FIG. 1  shows the power take-off device  1  for a farm vehicle of the present invention is fitted to a frame  2  of the vehicle, and comprises an output shaft  3 , which is fitted through a lateral wall  4  of frame  2  to rotate about an axis  5 , and has a grooved free end projecting outwards and defining a power take-off end  6  connectable angularly (in known manner) to a drive member (not shown), normally a universal joint, to transmit power from output shaft  3  to a machine or trailer (not shown). 
         [0019]    Upstream from output shaft  3 , device  1  comprises a drive  7  interposed between output shaft  3  and first and second input shafts  8  and  9 . The first input shaft  8  is an output shaft of the engine (not shown) and rotates about an axis  10  parallel to axis  5 . The second input shaft  9  is an output shaft of the vehicle transmission  11 , and rotates about an axis  12  parallel to axes  5  and  10 . 
         [0020]    More specifically, as shown in  FIG. 1 , the second input shaft  9  is supported for rotation by frame  2 , and is fitted on its free end with a bevel pinion meshing with an output gear of transmission  11 . Close to the pinion, The second input shaft  9  is fitted with a gear  13  meshing with a gear  14  which, together with gear  13 , forms part of drive  7 , is supported for rotation by frame  2 , and is fitted in rotary manner, by means of rollers, to a hollow body  15  which is fixed with respect to frame  2 , is coaxial with axis  10 , and houses shaft  8  in rotary manner. 
         [0021]    Drive  7  also comprises two shafts  16  and  17  coaxial with each other and with axis  10 , and extending from an end portion  18  of shaft  8  projecting axially from hollow body  15 , to lateral wall  4 , which is a hollow wall defined by an outer wall and an inner wall parallel to each other, perpendicular to axis  5 , and spaced apart to form a cavity  19  in between. 
         [0022]    Shaft  16  is hollow and is of substantially the same diameter as end portion  18  of shaft  8 , and is fitted in rotary manner through the inner wall of lateral wall  4 , and is fitted rigidly, on its free end inside cavity  19 , with a gear  20  meshing with a gear  21  fitted to output shaft  3 . 
         [0023]    As shown in  FIG. 1-9 , at the opposite end to that supporting gear  20 , shaft  16  has external teeth  22  coaxial with axis  10  and with a pitch diameter equal to the diameter of shaft  16 . 
         [0024]    Shaft  17  is mounted for rotation inside shaft  16 , and, at the end facing shaft  8 , has an end portion projecting axially from shaft  16  and inserted in a rotary manner inside a cavity  23  formed axially in the end portion  18  of shaft  8 . 
         [0025]    Shaft  17  is fitted with a toothed ring  24  coaxial with axis  10  in the gap between end portion  18  and shaft  16 , and which has external teeth  24   a  with the same pitch and pitch diameter as teeth  22  and further teeth  25  on end portion  18  facing teeth  24   a.    
         [0026]    At the opposite end to that fitted with toothed ring  24 , an end portion of shaft  17  projects axially from shaft  16 , is fitted in rotary manner, by means of a bearing, through the outer wall of lateral wall  4 , and is fitted, inside cavity  19 , with a gear  26  meshing with a gear  27  fitted to output shaft  3 . 
         [0027]    As explained below, shafts  16  and  17  are connectable angularly and selectively to shafts  8  and  9  to connect output shaft  3  angularly to shaft  8  or  9  and accordingly rotate end  6  at different speeds. 
         [0028]    Shafts  16  and  17  are connected angularly to shafts  8  and  9  by means of a selector defined by a sleeve  28 , which is coaxial with axis  10 , is fitted at least partly on end portion  18 , and is movable axially between five settings: three work settings corresponding to respective angular speeds of end  6 ; and two intermediate idle settings between the three work settings and corresponding to respective neutral positions of end  6 . 
         [0029]    As shown in  FIGS. 2-6 , face teeth  29  are formed on the annular end surface of sleeve  28  facing gear  14 , and mesh with like face teeth  30  formed on the annular end surface of gear  14  facing sleeve  28 . 
         [0030]    In addition to face teeth  29 , sleeve  28  also has internal teeth  31  close to face teeth  29 , coaxial with axis  10 , and meshing with teeth  25  on end portion  18 ; sleeve  28  also has internal teeth  32  formed on the opposite axial end of sleeve  28  to teeth  31 , and which are similar to teeth  31 , and mesh selectively with teeth  24   a  of shaft  17  and teeth  22  of shaft  16 . 
         [0031]    An annular groove  33  in the outer lateral surface of sleeve  28  is engaged, in use, by a known fork (not shown), which is connected by a drive (not shown) to a control lever (not shown) in the vehicle cab to move sleeve  28  between the five selection settings when the control lever is operated by the user. 
         [0032]    Operation of device  1  will now be described, as of the  FIGS. 2 and 7  work setting, in which end  6  is rotated by shaft  9 , via drive  7 , at an angular speed V 1 , which is proportional to the speed of shaft  9 , and therefore to the angular speed of the vehicle wheels, and therefore known as “ground speed”. 
         [0033]    In this setting, sleeve  28  is positioned so that face teeth  29  mesh with face teeth  30  of gear  14 , and teeth  32  mesh with teeth  24   a  of shaft  17 . 
         [0034]    Accordingly, rotation is transmitted from shaft  9  to shaft  17  by gears  13  and  14  and sleeve  28 , and from shaft  17  to output shaft  3 , i.e. end  6 , by gears  26  and  27 . 
         [0035]    The ratio between angular speed V 1  and the angular speed of shaft  9  therefore equals gear ratio: 
         [0000]        T   1 =( R   13   /R   14 )×( R   26   /R   27 ) 
         [0000]    i.e. the ratio between the radii of gears  13  and  14  times the ratio between the radii of gears  26  and  27 . 
         [0036]      FIG. 3  shows the next setting after the  FIGS. 2 and 7  setting and corresponding to a neutral position of end  6 . In this setting, which is achieved by moving sleeve  28  axially rightwards from the previous setting, teeth  32  still mesh with teeth  24   a  of shaft  17 , but, since face teeth  29  no longer mesh with face teeth  30 , and teeth  31  no longer mesh with teeth  25  of shaft  8 , sleeve  28  receives no motion from either shaft  9  or shaft  8 , and so transmits no rotation to shaft  17 . 
         [0037]    Further rightward movement of sleeve  28  moves it into the  FIGS. 4 and 8  setting, in which output shaft  3  is connected angularly to shaft  8  by shaft  17 , and end  6  rotates at a speed V 2  of normally about 540 rpm. 
         [0038]    In this setting, teeth  31  of sleeve  28  mesh with teeth  25  of shaft  8 , and teeth  32  mesh with teeth  24   a  of shaft  17 , so that motion is transmitted from shaft  8  to shaft  17  by sleeve  28 , and from shaft  17  to output shaft  3  by gears  26  and  27 . 
         [0039]    The ratio between angular speed V 2  and the angular speed of shaft  8  therefore equals gear ratio: 
         [0000]    
       
      
       T 
       2 
       =R 
       26 
       /R 
       27  
      
     
         [0000]    i.e. the ratio between the radii of gears  26  and  27 . 
         [0040]    The next setting is shown in  FIG. 5 , and corresponds to a further neutral position of end  6 . 
         [0041]    In this setting, which is achieved by further rightward axial movement of sleeve  28 , teeth  31  still mesh with teeth  25  of shaft  8 , but teeth  32  mesh with neither teeth  24   a  nor teeth  22 , so that, despite sleeve  28  rotating at the angular speed of shaft  8 , rotation of sleeve  28  is transmitted to neither shaft  17  nor shaft  16 . 
         [0042]    As shown in  FIGS. 6 and 9 , further rightward movement of sleeve  28  moves it into a further setting, in which output shaft  3  is connected angularly to shaft  8  by shaft  16 , and end  6  rotates at a speed V 3  of normally about 750 or 1000 rpm. 
         [0043]    In this setting, teeth  31  of sleeve  28  mesh with teeth  25  of shaft  8 , and teeth  32  mesh with teeth  22  of shaft  16 , so that motion is transmitted by sleeve  28  from shaft  8  to shaft  16 , and from shaft  16  to output shaft  3  by gears  20  and  21 . 
         [0044]    The ratio between angular speed V 3  and the angular speed of shaft  8  therefore equals gear ratio: 
         [0000]    
       
      
       T 
       3 
       =R 
       20 
       /R 
       21  
      
     
         [0000]    i.e. the ratio between the radii of gears  20  and  21 . 
         [0045]    The device  1  provides for selecting three different angular speeds of end  6 , i.e. 540 rpm, 750 or 1000 rpm, and so-called “ground speed”, using only one selector defined by sleeve  28 . And since one sleeve also means one actuating fork and one control lever, this greatly simplifies operator control design and operation. 
         [0046]    Moreover, by transmitting motion using coaxial shafts  16  and  17 , sleeve  28  can be distanced from output shaft  3  and located in a more central position on the vehicle, closer to the operator cab, thus advantageously reducing and simplifying the drive between sleeve  28  and the control lever in the cab, with obvious advantages in terms of reliability and manufacturing cost.