BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a rotary shower head and particularly to a water-saving shower head. 
         [0003]    2. Description of the Prior Art 
         [0004]    Shower head, as the one shown in  FIG. 1 , is commonly used by people to save water in shower. It generally has a water discharge tray  1  with a plurality of water outlets  11  formed thereon to spray water while users are taking shower. To save water some shower heads have the water outlets  11  formed at a smaller size or with a fewer number. Such approaches have shortcomings in practice, notably: 
         [0005]    1. The water outlets  11  of a smaller size or fewer number produce less powerful water ejection or a smaller water covering area, hence give users non-thorough cleaning feeling. Users tend to increase showering time to compensate this deficiency. As a result, instead of water saving, more water consumption and waste occur. 
         [0006]    2. The water outlets  11  of a smaller size are easily clogged by impurities in the water. 
       SUMMARY OF THE INVENTION 
       [0007]    In view of the aforesaid problems, the present invention aims to provide a rotary shower head which has an outer case housing a universal joint, an inner case assembly, a driving mechanism and a water discharge disc. Water discharge thrusts the driving mechanism to generate automatic turning of the water discharge disc. Therefore a greater water spraying area is generated, and water-saving effect can be achieved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic view of a conventional shower head. 
           [0009]      FIG. 2  is an exploded view of the invention. 
           [0010]      FIG. 3  is a sectional view of the invention. 
           [0011]      FIG. 4  is a cross section of an embodiment of the invention. 
           [0012]      FIG. 5  is a fragmentary exploded view of an embodiment of the invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0013]    Please referring to  FIGS. 2 ,  3  and  5 , the present invention aims to provide a rotary shower head which includes an outer case  2  to house a universal joint  3 , an inner case assembly  4 , a driving mechanism  5  and a water discharge disc  6 . 
         [0014]    The outer case  2  has a housing chamber  21  to hold the following elements and an opening  22  at a top end thereof. 
         [0015]    The universal joint  3  includes:
       a cap  31  which has an aperture  311  with a first thread portion  312  formed on an inner side; and   a ball seat  32  which has a body run through by a screw hole  321 , and a ball  322  at one end and a first fastening section  323  at another end extended outside the aperture  311  of the cap  31  and the opening  22  of the outer case  2 .       
 
         [0018]    The inner case assembly  4  includes:
       an upper case  41  which has a housing compartment  411  with an inner rim formed a plurality of retaining ribs  412 , and a coupling portion  413  at one end to hold the ball  322  of the ball seat  32 . The coupling portion  413  has at least one diagonal hole  414  and a first axle hole  415  at the bottom leading to the housing compartment  411 . The coupling portion  413  further has a second thread portion  416  on an outer side fastenable to the first thread portion  312  of the cap  31 . The upper case  41  also has a lower end formed a third thread portion  417  on the outer side; and   a lower case  42  which has a through hole  421  in the center that has a jutting annular rib  422  on the circumference and a fourth thread portion  423  on an inner side fastenable to the third thread portion  417 .       
 
         [0021]    The driving mechanism  5  includes:
       a rotary disc  51  which has a first gear shaft  511  extended form the center of the bottom and formed with a second axle hole  512 , and a plurality of vanes  513 ;   an upper lid  52  which is held in the inner case assembly  4 , and has a third axle hole  521  run through by the first gear shaft  511  and retained by a retaining ring A. The third axle hole  521  is surrounded by an annular flange  522  to hold the rotary disc  51 . The upper lid  52  further has a first fastening portion  523  on the bottom side;   a first speed-reducing set  53  which includes a first bottom disc  531  and a plurality of first gears  532 . The first bottom disc  531  has a second gear shaft  5311  extended downwards from the center of the bottom thereof and a fourth axle hole  5312  corresponding to the second axle hole  512 . The first bottom disc  531  further has a plurality of first struts  5313  around the fourth axle hole  5312  to hold the first gears  532  to engage with the first gear shaft  511  of the rotary disc  51  to form chain movement;   a second speed-reducing set  54  which includes a second bottom disc  541  and a plurality of second gears  542 . The second bottom disc  541  has a third gear shaft  5411  extended downwards from the center of the bottom thereof and a fifth axle hole  5412  corresponding to the fourth axle hole  5312 . The second bottom disc  541  further has a plurality of second struts  5413  to hold the second gears  542  to engage with the second gear shaft  5311  to form chain movement;   a seat  55  which has a housing space  551  to hold the first and second speed-reducing sets  53  and  54 , and a second fastening portion  552  at the top side to fasten to the first fastening portion  523  of the upper lid  52 . The seat  55  also has a boss  555  at the bottom that has a sixth axle hole  553  run through by the third gear shaft  5411  of the second bottom disc  541 . The housing space  551  has an annular gear rack  554  on an inner rim to engage with the gears  532  and  542  of the first and second speed-reducing sets  53  and  54 . The boss  555  has at least one hole  556  formed on the periphery. The seat  55  further has a plurality of retaining lugs  557  formed on the perimeter corresponding to and latchable with the retaining ribs  412  of the upper case  41  so that the seat  55  can be retained as desired;   a rotary head  56  which has a coupling trough  561  in the center that has an internal gear rack  562  to engage with the third gear shaft  5411  to generate chain movement. The coupling trough  561  further has a seventh axle hole  563  at the bottom. The rotary head  56  also has an annular base  564  with at least one ridge  565  formed on the perimeter and a plurality of orifices  566  formed thereon; and   an axle  57  running through the first, second, fourth, fifth and seventh axles  415 ,  512 ,  5312 ,  5412  and  563 .       
 
         [0029]    The water discharge tray  6  includes:
       a pad  61  which has a hole  611  in the center and a plurality of jutting water discharge struts  612  each has a water outlet  613  running through;   a face disc  62  which has an anchor boss  621  in the center to couple with the hole  611  of the pad  61  and a plurality of coupling holes  622  mating and run through by the water discharge struts  612 ; and   a bottom seat  63  which has a disc  631  and a transmission portion  632  in the center of the disc  631 . The transmission portion  632  has a plurality of annular latch grooves  633  inside latched by the ridge  565  of the rotary head  56  to form chain movement.       
 
         [0033]    Referring to  FIGS. 2 through 5 , by means of the structure set forth above, when in use water enters through the ball seat  32  into the coupling portion  413  of the upper case  41 ; the entering water passes through the diagonal holes  414  and generates a diagonal thrust force to drive the vanes  513  and turn the rotary disc  51 ; the entering water flows out through space at two sides of the rotary disc  51  so that the first gear shaft  511  also drives the first gears  532  of the first speed-reducing set  53  and the first bottom disc  531 , and the second gears  542  of the second speed-reducing set  54  and the second bottom disc  541  and the third gear shaft  5411  also are driven to rotate, and consequently the bottom seat  63  also is driven to rotate. As a result the entire water discharge tray  6  rotates so that the water is discharged through the water outlets  613  of the water discharge struts  612  with moving spraying spots. The number of the water outlets  613  can be reduced (without shrinking the size thereof) to save water consumption, while the effective spraying area can be increased to enable users to take shower and get thorough cleaning of their bodies.
A rotary shower head for showering includes an outer case to house a universal joint, an inner case assembly, a driving mechanism and a water discharge disc. Water entering the shower head provides a water discharge force to thrust the driving mechanism to generate automatic turning of the water discharge disc to achieve water-saving effect.