Abstract:
A method of manufacturing a compressor valve plate ( 36 ) comprises at least the following steps in succession: blanking of a blank of the plate ( 36 ) from a steel sheet of suitable thickness, punching holes corresponding to the output and intake openings, the hole corresponding to the output opening being a preliminary hole ( 48   a ) having a diameter larger than the final diameter of this opening ( 48 ), forming, by coining, a depression ( 42 ) for housing an output valve-closure blade ( 54 ), with the depth of the depression increasing towards the end of the depression which corresponds to the preliminary hole ( 48   a ), in a manner such that, during the coining, at least some of the material of the blank creeps towards the preliminary hole, partially filling it, calibrating the output opening ( 48 ) to the final diameter by punching, and coining an annular projection ( 50 ) around the calibrated output opening ( 48 ) to define a valve seat for the output closure blade.

Description:
This is a National stage entry under 35 U.S.C. § 371 of Application No. PCT/EP01/01918 filed Feb. 20, 2001, the above noted prior applications are all hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to automatic valves used in compressors, particularly in hermetic motor-driven compressors for refrigerators and the like. 
   In these compressors, a valve plate having an intake opening and an output opening is clamped between the cylinder and the manifold head. A respective closure element constituted by an elongate, resiliently flexible metal blade is associated with each of the openings. 
   One end of each of these blades cooperates with the respective opening and the other end is fixed to the plate. The closure blade of the output valve is fixed to the face of the plate remote from the piston and facing towards the head. This blade bends towards the head, moving away from the output opening when the piston expels the fluid from the cylinder. 
   During the intake and compression of the fluid, the closure blade of the output valve is fitted against an annular projection which surrounds the output opening. 
   Any measure for improving the performance of a motor-driven compressor for refrigerators and the like, with a consequent, even small, saving in electrical energy, is welcome. 
   One of these measures consists in reducing as far as possible the so-called clearance volume, that is, the space existing between the valve plate and the piston. 
   Part of this clearance volume is formed by the output opening which always remains in communication with the interior of the cylinder, given that the respective closure element closes it on the face of the valve plate facing towards the output manifold head. 
   SUMMARY OF THE INVENTION 
   It is therefore advantageous to shorten the axial length of the output opening as much as possible. This can be achieved by the formation, in the outer face of the plate, of a depression in which the output opening opens and in which the output closure blade is housed. An example of this solution is given by the document U.S. Pat. No. 2,647,683. 
   This depression can be produced by coining with a flat punch which forms the depression with the same depth throughout. 
   The preamble to claim  1  takes account of this prior art. 
   However, the known technique has the following disadvantages:
         coining with a flat punch requires a large coining force since all of the material of the depression is made to creep at the same time,   owing to the large forces involved, the coining punch wears very quickly.       

   The main object of the invention is to provide a method which eliminates this disadvantage. 
   According to the invention, this object is achieved by means of a method as claimed. 
   By virtue of the concept of the invention, the punch which performs the coining of the depression for housing the output closure blade is pressed into the material of the valve plate progressively with relatively small coining forces and hence with little wear, causing this material to creep predominantly into the region in which the output opening is disposed. This is in fact the only region in which it is advantageous to reduce the thickness of the valve plate in order to reduce the axial length of the output opening as far as possible. 
   As claimed in claim  2 , this operation can preferably be performed in successive steps. 
   After the or each coining of the depression, the metal which has spread into the hole of the output opening by creeping is removed by a punching operation to produce a calibrated output opening. 
   The invention also relates to a valve plate produced by the method claimed, a valve unit comprising a valve plate produced by the method, as well as a compressor, particularly for refrigerating machines, which comprises the said valve plate or the said valve unit. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will become clearer from a reading of the following detailed description, given with reference to the appended drawings, provided by way of non-limiting example, in which: 
       FIG. 1  is a partially-sectioned, partial elevational view of a hermetic compressor for refrigerators and the like, incorporating a valve unit according to the invention, 
       FIG. 2  is an exploded, perspective view of the valve unit of the compressor viewed from the side facing towards the output manifold head of the compressor, 
       FIG. 3  is an exploded, perspective view of the same valve unit viewed from the side facing towards the cylinder of the compressor, 
       FIGS. 4 to 9  are schematic partial sections of a valve plate of the unit of  FIGS. 2 and 3 , showing successive steps of the processing of the plate, 
       FIG. 10  is a partial plan view taken on the arrow X of  FIG. 9 , showing the region of the valve plate in which the depression for the output valve has been produced during the step of  FIG. 9 , and 
       FIG. 11  is a section similar to that of  FIGS. 4 to 9 , showing a last step of the processing of the valve plate. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With reference to  FIG. 1 , a hermetic motor-driven compressor comprises a hermetic casing  10  in which the actual motor-driven compressor, generally indicated  12 , is housed. 
   The motor-driven compressor  12  comprises an electric motor  14  with a stator assembly  16  suspended in the casing  10 . 
   The housing  18  of a positive-displacement compressor is fixed to the upper portion of the stator assembly  16 . 
   A crankshaft  20  is supported rotatably in the housing  18  and a connecting rod  22  is connected thereto. The connecting rod  22  in turn is coupled to a horizontal piston  24  slidable in a cylinder  26  formed in the housing  18 . 
   The cylinder  26  terminates in a head end constituted by a flange  28  having a substantially square shape in plan. 
   A head unit or valve unit  30 , which will be referred to further below, is fixed to the flange  28 . 
   An output manifold head  32  and an intake silencer  34  are associated with the valve unit  30 . 
   With reference to  FIGS. 2 and 3 , the valve unit  30  of  FIG. 1  comprises, basically, a square valve plate  36  made of thick steel plate. 
   Through-holes  38  are punched in the four corners of the plate  36  for its fixing, by means of screws, to the flange  28  of the cylinder  26 , together with the output manifold head  32  ( FIG. 1 ). 
   The holes  38  may be punched separately, or simultaneously with one of the punching operations which will be referred to further below. 
   With reference to  FIG. 2 , a depression  40  with a substantially L-shaped profile comprising a longer arm  42  and a shorter arm  44  is formed in the face of the plate  36  which is to face towards the output manifold head  32  of  FIG. 1 . 
   An end portion  46  of the longer arm  42  remote from the smaller arm  44  is enlarged, with a substantially circular shape. 
   An output through-opening  48 , also visible in  FIG. 3 , opens in the base of this end portion  46 . The output opening  48  is surrounded by an annular projection  50  which projects from the base of the enlarged portion  46 . 
   A pair of bosses  52 , the function of which will be explained below, projects from the base of the shorter arm  44 . 
   The depression  40  houses an output closure blade  54  having an L-shape substantially corresponding to that of the depression  40  and comprising a longer arm  56  and a shorter arm  58 . 
   An end portion  60  of the longer arm  56  remote from the shorter arm  58  is enlarged with a substantially disk-like shape to constitute an actual closure element for cooperating with the annular projection  50 . 
   A pair of holes  62  corresponding to the bosses  52  is formed in the shorter arm  58 . 
   The output closure blade  54  is covered by a travel limiter  64  which is also substantially L-shaped with a longer arm  66  and a shorter arm  68 . 
   A pair of holes  70  corresponding to the holes  62  of the closure blade  54  and to the bosses  52  is formed in the shorter arm  68 . 
   In the assembled condition, the shorter arm  58  of the blade  54  and the shorter arm  68  of the limiter  64  are held firmly in the shorter arm  44  of the depression  40  by virtue of the fact that the bosses  52  are fitted in the holes  62  and  70  and are upset like rivets onto the shorter arm of the limiter  64 . 
   With reference to  FIG. 3 , a substantially T-shaped shallow depression  72  comprising a longitudinal arm  74  and a transverse arm  76  is formed in the face of the plate  36  facing the cylinder  26  of  FIG. 1 . 
   An end portion  78  of the longitudinal arm  76  is enlarged, with a substantially circular shape. 
   An intake through-opening  80 , also visible in  FIG. 2 , opens in this end portion  78 . 
   The opening  80  is also surrounded by an annular projection  82 . 
   A pair of bosses  84  projects from the base of the transverse arm  76 . 
   The depression  74  houses an intake closure blade  84  having a T-shaped profile corresponding to that of the depression  74  and comprising a longitudinal arm  86  and a transverse arm  88 . 
   An end portion  90  of the longitudinal arm  86  remote from the transverse arm  88  is enlarged with a substantially circular shape and cooperates with the annular projection  82 , as a closure element. 
   The transverse arm  88  has a pair of holes  92  in which the bosses  84  are fitted. 
   The bosses  84  are upset like rivets onto the transverse arm  88  in order to restrain the intake closure blade  84  firmly. 
   Reference will now be made to  FIGS. 4 to 11  to describe the processing to which the plate  36  is subjected in order to form the depression  40  of the output valve as well as, preferably, the bosses  52  of  FIG. 2  and the bosses  84  of  FIG. 3 . 
   In all of  FIGS. 4 to 9  and  11 , a support surface, which may not be the same in all of the operations that will be described, is conventionally indicated  94 . 
   The steps of the blanking of a blank of the plate  36  from a steel sheet, of the punching of its corner holes  38  and of its intake opening  80 , and of the coining of the depression  74  and the annular projection  82  of  FIG. 3  for the intake valve will not be described since they are conventional. 
   In  FIG. 4 , a punch  96  forms, by punching in the plate  36 , a preliminary hole  48   a  corresponding to the output opening  48  but having a diameter larger than the final diameter of this opening. 
   In  FIG. 5 , a coining punch, indicated  98 , has an active surface  100  which is inclined to the support surface  94  with a slope converging towards the already-punched hole  48   a  ( FIG. 4 ). 
   The flat active surface  100  terminates in an arcuate active surface  102  at an end corresponding to the hole of the output opening. 
   A first coining of the depression  42 , indicated  42   a  in  FIG. 5 , is performed with the punch  98 , conferring on the depression a depth which increases from the end remote from preliminary hole  48   a  of  FIG. 4  (that is, corresponding to the shorter arm  44  of  FIG. 2 ). 
   The first coining operation of  FIG. 5  causes the material of the plate  36  to creep, as a result of which this material partially spreads into the preliminary hole and makes it smaller, more or less as shown at  48   b  in  FIG. 5 . 
   In  FIG. 6 , a second punch  104  performs a second punching of the preliminary hole  48   b  of  FIG. 5  which brings its diameter substantially back to the value achieved in the punching step of  FIG. 4 , as shown at  48   c.    
   In  FIG. 6 , the depression is again indicated  42   a.    
   In  FIG. 7 , a second coining of the depression, now indicated  42   b , is performed by means of a second coining punch  106  of a shape substantially identical to that of the punch  98  of  FIG. 5 . 
   In this case also, the material of the plate  36  is displaced by creeping and partially spreads into the hole  48   c  of  FIG. 6 , as indicated at  48   d.    
   During the step of  FIG. 8 , a third punch  108  performs a third, final calibrating punching of the preliminary hole to the diameter of the output opening, now indicated  48 . 
   As can already be seen in  FIG. 8 , by virtue of the formation of the depression  42 , the finished output opening  48  has an axial length equal to less than half of the thickness of the plate  36 . 
   In  FIG. 9 , a further coining punch  110  forms the annular projection  50  of  FIG. 2  around the opening  48 . 
   The configuration of the punch  110  is such as to deform the depression  42  in accordance with the configuration shown in  FIG. 10 , in which the projection is again indicated  50 . 
   The base of the depression  42  is deformed, during the third coining, both in a region  42   a  surrounding the annular projection  50  and in lateral regions  42   b . These lateral regions  42   a  extend towards the shallower end of the depression  42  which corresponds to the region of the fixing of the output closure blade  54  of  FIG. 2 , that is, to the shorter arm  44 . 
   However, the surfaces of the projection  50 , of the fixing region  44 , and of a central strip  42   c  of the base of the depression disposed between the lateral regions  42   b  are left in a common inclined plane by the punch  110 . 
   The central strip  42   c  is separated from the projection  50  and is connected to the fixing region or shorter arm  44 . 
   The projecting surfaces thus produced, which are shown by speckling in  FIG. 10 , form part of an inclined plane on which the output closure blade  54  of  FIG. 2  bears when the output valve is closed. 
   The punch  110  preferably but not necessarily has a shaped recess  112  which, in cooperation with a counter-punch  114 , forms the two bosses  52  for the fixing of the output closure blade  54 . 
     FIG. 9  also shows a recess  116  in the support surface  94  for cooperating with a punch  118  to form the bosses  84  for the fixing of the intake closure blade  84  ( FIG. 3 ). 
   The bosses  84  may also be formed separately from the coining operation of  FIG. 9 . 
   In  FIG. 11 , a further punch  120  with an active surface  122  inclined in the same manner as those of the punches  98 ,  106 ,  110 , performs a light final finishing coining both of the projecting regions  44  and  42   c  of the depression  42  and of the annular projection  50 , leaving the already finished output opening  48  unchanged. 
   In a simpler embodiment of the method, the processing of the valve plate  36  could comprise a single step such as that of  FIG. 5  for the coining of the depression, and a single subsequent step such as that of  FIG. 8  for the calibration of the output opening  48 .