Patent Abstract:
Piezoelectric pump for a household electric appliance having a moving wall interposed between a first casing element defining a pumping chamber with the moving wall, and a second casing element applying pressure to the periphery of the moving wall in order to hold the latter in position. The moving wall has an exterior face in contact with a piezoelectric actuator designed to cause the moving wall to move so as to bring about a periodic variation in the volume of the pumping chamber under the action of the piezoelectric actuator wherein the first casing element and the second casing element are held together under stress by an elastic clip, the elastic clip applying a pressure that tends to compress the first casing element onto the second casing element.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a piezoelectric pump for a household electric appliance and more particularly relates to a piezoelectric pump comprising a moving wall interposed between a first casing element, defining a pumping chamber with the moving wall, and a second casing element applying pressure to the periphery of the moving wall in order to hold the latter in position. 
     2. Description of Related Art 
     Japanese patent application #62142597 discloses a clothing iron comprising a piezoelectric pump that supplies a vaporization chamber with water from a receptacle. This document describes a piezoelectric pump comprising a moving wall interposed between a first element, defining a pumping chamber with the moving wall, and a second element applying pressure to the periphery of the mobile wall in order to hold the latter in position. 
     In a customary fashion, the first and second casing elements are fastened together by gluing, screwing, or ultrasound welding. Such assembly means, however, have the disadvantage of allowing a certain degree of relaxation of the pump elements over time, particular under the effect of temperature fluctuations. This phenomenon is accentuated when the elements of the piezoelectric pump are made of plastic. 
     The performance of a piezoelectric pump is closely linked to the dimensions of the pumping chamber. Hence the phenomenon of relaxation of the means for assembling the various parts of the casing can lead to a significant decline in pump performance. These same factors make it equally difficult to mass produce piezoelectric pumps with uniform performance characteristics. 
     SUMMARY OF THE INVENTION 
     Hence an object of this invention is to remedy these disadvantages by proposing a piezoelectric pump in which the assembly of the pump elements makes it possible to obtain a pumping chamber with stable performance characteristics over time. 
     To this end, the object of the invention is a piezoelectric pump for a household electric appliance comprising a moving wall interposed between a first casing element, defining a pumping chamber with the moving wall, and a second casing element applying pressure to the periphery of the moving wall in order to hold the latter in position, said moving wall comprising an exterior face in contact with a piezoelectric actuator designed to cause said moving wall to move so as to bring about a periodic variation in the volume of the pumping chamber by means of said piezoelectric actuator, characterized in that said first casing element and said second casing element are held together under stress by means of an elastic clip applying a pressure that tends to compress said first casing element onto said second casing element. 
     According to another characteristic of the invention, a gasket is interposed between the moving wall and the first casing element. 
     According to still another characteristic of the invention, the second casing element comprises a raised portion that applies pressure to the moving wall opposite the gasket, thus sandwiching the periphery of said moving wall between said gasket and said raised portion. 
     According to still another characteristic of the invention, the moving wall comprises a bottom face coated with at least one electrically insulating adhesive film that extends radially beyond the moving wall and has a peripheral rim glued onto the second casing element. 
     According to another characteristic of the invention, the elastic clip comprises a part that exerts pressure on the second casing element, in the zone opposite the pumping chamber. 
     According to another characteristic of the invention, the elastic clip comprises at least one end with a gripping tab. 
     According to another characteristic of the invention, the elastic clip consists of a springy metal band. 
     According to another characteristic of the invention, the first and second casing elements comprise complementary shapes that ensure their correct relative positioning during the assembly of the pump by means of the elastic clip. 
     According to another characteristic of the invention, the piezoelectric pump comprises a third element covering the first element oppositely disposed relative to the second element, said third element comprising a delivery line and a discharge line communicating with an inlet and an outlet, respectively, of the pumping chamber. 
     According to another characteristic of the invention, the first and third elements comprise complementary shapes that ensure their correct relative positioning during the assembly of the piezoelectric pump by means of the elastic clip. 
     According to another characteristic of the invention, the elastic clip presses on the second and third elements. 
     The invention further relates to a clothing iron comprising means for supplying water to a spray nozzle or to a vaporization chamber, characterized in that said supply means comprise a piezoelectric pump as described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects, aspects, and advantages of the present invention will emerge more clearly from the following description of an illustrative embodiment of the invention provided as a nonlimiting example, with reference to the appended drawings, in which: 
         FIG. 1  is a schematic cutaway view of a clothing iron equipped with a pump according to a first embodiment of the invention; 
         FIG. 2  is a cutaway view of the piezoelectric pump of the appliance of  FIG. 1 ; 
         FIGS. 3 and 4  are exploded perspective views of the piezoelectric pump of  FIG. 2 , as viewed from above and viewed from below, respectively; 
         FIG. 5  is a perspective view of the assembled pump of  FIG. 2 ; 
         FIG. 6  is a cutaway view of a pump according to a second embodiment of the invention; 
         FIG. 7  is an exploded perspective view of the pump of  FIG. 6 ; 
         FIGS. 8 and 9  are perspective views of the assembled pump of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Only the elements needed for understanding the invention have been shown. To make the drawings easier to read, the same elements have the same reference numbers from figure to figure. 
       FIG. 1  is a schematic illustration of a clothing iron  100  comprising a heating sole  104  that includes a vaporization chamber  103  supplied with water by a piezoelectric pump  101  connected to a receptacle  102 . 
     The piezoelectric pump  101 , shown separately in  FIGS. 2-4 , comprises a first casing element consisting of a support  1  made of a plastic reinforced with glass fibers, such as a polyarylamide with 30% glass fiber reinforcement. The support  1  has a circular center zone  1 A defining, with a moving wall  4  disposed face to face, a pumping chamber  5 , wherein said moving wall advantageously consists of a brass membrane  4  comprising an exterior face oriented toward the exterior of the pumping chamber  5 , on which is attached a ceramic piezoelectric actuator  41 . 
     The support  1  is sandwiched between a second and a third casing element made of the same material as the one used for the support  1 ; said second and third casing elements consisting, respectively, of a lid  2  comprising terminals  23 ,  24  for supplying electricity to the piezoelectric actuator  41  and of a base plate  3  allowing the circulation of the fluid in the pumping chamber  5 . 
     The terminals  23  and  24  are in contact with a spring  23 A contacting the membrane  4  and a spring  24 A contacting the piezoelectric actuator  41 , respectively, and are powered by an a.c. voltage that brings about a periodic deformation of the piezoelectric actuator  41  in the direction for increasing and then for decreasing the volume of the pumping chamber  5 . 
     The supply voltage for the piezoelectric actuator  41  is preferably provided directly from the household mains via a supply circuit (not shown in the figures) that is not equipped with an isolation transformer. An example of such a supply circuit for the piezoelectric pump is described in French patent application #08 01706. 
     In order to ensure electrical insulation between the membrane  4  subjected to the mains voltage and the water present in the pumping chamber  5 , the bottom face of the membrane  4  is coated with an insulating film  4 A consisting of three polyester layers held together by means of an adhesive, in accordance with the solution described in French patent application #08 03520. 
     As can be more easily discerned in  FIGS. 2 and 3 , the base plate  3  of the pump  101  comprises a delivery line  31  and a discharge line  32  emerging opposite an inlet  11  and an outlet  12  piercing the support  1 , respectively. 
     The inlet  11  and the outlet  12  are advantageously connected to each other by a channel  13  with a depth of around 1 mm and extending along the top face of the support  1  and defining a dead volume in the pumping chamber  5 . 
     The pumping chamber  5  is laterally delimited by an annular gasket  6  placed in a circular channel  14  formed on the top face of the support  1 , the membrane  4  resting on the gasket  6  and having a circular shape with a diameter adapted for engaging precisely between guide ribs  15 A borne by a raised centering sleeve  15  on the top face of the support  1 . By way of an example, the gasket  6  is a four-lobed seal with an inner diameter of around 22 mm and a height of around 2 mm. 
     The membrane  4  is held against the gasket  6  by means of the lid  2 , the latter comprising a bottom face with a circular rib  21  with a diameter that corresponds to the diameter of the gasket  6  such that the bottom edge of the circular rib  21  is pressed against the exterior face of the membrane  4  opposite the gasket  6 . In order to facilitate the deformation of the membrane  4  by means of the piezoelectric actuator  41 , the bottom edge of the circular rib  21  advantageously has a convergent, rounded shape. 
     According to  FIGS. 2 and 4 , the lid  2  extends radially beyond the rib  21 , forming a wall  20  that abuts with the top end of the centering sleeve  15  when the membrane  4  is compressed against the gasket  6 , said centering sleeve  15  and said circular rib  21  being dimensioned such that the membrane  4  is located in immediate proximity to the top face of the support  1 ; for example, at a distance of around 0.1 mm, when the wall  20  of the lid  2  is in abutment with said centering sleeve  15 . 
     The lid  2  is also equipped with a circular, peripheral skirt  22  extending axially towards the support  1  and the bottom edge of which compresses an o-ring gasket  7  resting on a shoulder  16  of the support  1 . Said o-ring gasket  7  has the advantage of creating a second seal that ensures the confinement of the liquid in the casing of the pump  101  in case there is a leak around the gasket  6 . 
     According to  FIGS. 3 and 4 , the positioning of the lid  2  relative to the support  1  is achieved by means of three aligning studs  15 B projecting from the top end of the centering sleeve  15  of the support  1 , said three aligning studs  15 B engaging in corresponding cavities  20 A of the bottom face of the lid  2 , wherein one of the studs  15 B has a greater width for allowing the lid  2  to engage on the support  1  in one direction only. 
     The positioning of the base plate  3  on the support  1  is in turn achieved by means of bosses  30  borne on the top face of the base plate  3 , which engage in corresponding cavities  10  on the bottom face of the support  1 , wherein one of the bosses  10  is larger in size for allowing the base plate  3  to engage on the support  1  in one direction only. 
     The inlet  11  and the outlet  12  of the pumping chamber  5  are equipped with valves  81 ,  82  formed in a silicone film  8  interposed between the support  1  and the base plate  3 , said film comprising cut-outs  80  that engage around the bosses  30  in order to ensure the correct positioning of said film  8  on said base plate  3 . 
     The valve  81 , which consists of a horseshoe-shaped cut opposite the inlet  11 , closes when the water in the pumping chamber is compressed by the membrane  4  and opens when the piezoelectric actuator  41  bends in the direction for increasing the volume of the pumping chamber  5 . 
     The valve  82 , which also consists of a horseshoe-shaped cut opposite the outlet  12 , opens when water is compressed in the pumping chamber  5  and closes when the piezoelectric actuator  41  bends in the direction for increasing the volume of the pumping chamber  5 . 
     More particularly according to the invention and according to  FIG. 5 , the support  1 , the lid  2 , and the base plate  3  are held together under stress by means of an elastic clip  9  preferably consisting of a springy metal band with a width of around 8 mm. 
     The elastic clip  9  has the general shape of a “U”, of which the inwardly curved ends form hooks  91  that hook under the base plate  3 , the clip  9  comprising a center part  90  that exerts pressure over a whole center zone  2 A of the lid  2 , thus generating a force in the axis of the circular rib  21  pressing on the periphery of the membrane  4 . 
     The lid  2  and the base plate  3  advantageously comprise guide ribs  25 ,  35  on their peripheries, said guide ribs  25 ,  35  delimiting a track in which the elastic clip  9  engages in order to ensure a correct positioning of said clip  9 . 
     According to  FIG. 2 , the center zone  2 A of the lid has a reinforced rigidity so that the pressure exerted by the clip  9  is integrally transmitted via the circular rib  21  to the periphery of the membrane  4  rather than causing the lid  2  to bend. To this end, the lid  2  has a concave bottom face in the center zone  2 A delimited by the circular rib  21 , the lid  2  exhibiting a thickness of around 1.4 mm in its center and a thickness of around 2 mm near the circular rib  21 . 
     One of the hooks  91  of the clip  9  preferably extends to form an outwardly curved gripping tab  91 A that makes it possible to grasp and bend the clip  9 , thus making it easier to fasten said clip  9  around the lid  2  and onto the base plate  3 , or to remove it therefrom. 
     The pump  101  thus configured has the advantage of possessing a flexible membrane  4  supporting the piezoelectric actuator  41 , the periphery of which is subjected to a substantially constant pressure over time, the elastic clip  9  keeping the lid  2  pressed against the support  1  and the gasket  6 . Furthermore, the pressure applied by the clip  9  has the advantage of being equally distributed over the entire periphery of the membrane  4 , making it possible to achieve optimum performance of the pump  101 . 
     This particular assembly enables the achievement of a pump that is cheap to manufacture and that exhibits stable performance over time. Lastly, a pump equipped with such a fastening clip also has the advantage that it can be assembled or dismantled quickly, notably for maintenance. 
       FIGS. 6-9  show a piezoelectric pump  200  according to a second special embodiment of the invention in which the electrical insulation of the pump, and particularly the insulation of the hydraulic part from the part subjected to an electric potential, has been improved. 
     According to  FIG. 6 , the pump  200  comprises a support  201  made of plastic reinforced with glass fibers that comprises a circular center zone defining, with a circular brass membrane  204  attached face to face, a pumping chamber  205 . 
     The support  201  is sandwiched between a lid  202  comprising terminals  223 ,  224  for supplying electric power to a piezoelectric actuator  241  fastened onto the membrane  204  and a base plate  203  allowing the circulation of fluid in the pumping chamber  205 . 
     The electric terminals  223  and  224  are electrically connected to the membrane  204  and to the piezoelectric actuator  241 , and are powered by an a.c. voltage that brings about a periodic deformation of the piezoelectric actuator  241  and of the flexible membrane  204  in the direction for increasing and then for decreasing the volume of the pumping chamber  205 . 
     In order to ensure electrical insulation between the parts of the pump  200  subjected to an electric potential and the liquid contained in the pumping chamber  205 , the bottom face of the membrane  204  is coated with an insulating film  204 A consisting of three polyester layers held together by means of an adhesive, as described in more detail in French patent application #08 03520. Said insulating film  204 A has the shape of a disc with a diameter greater than the diameter of the membrane  204  such that said insulating film  204 A comprises a peripheral portion that extends radially beyond the membrane  204  by ca. 5 mm. 
     The hydraulic coupling of the pump  201  is achieved by means of a delivery line  231  and a discharge line  232  borne by the base plate  203 , said delivery  231  and discharge  232  lines emerging opposite an inlet  211  and an outlet  212  piercing the support  201 , respectively. 
     According to  FIG. 6 , the pumping chamber  205  is laterally delimited by an annular gasket  206  similar to the gasket  6  described for the first embodiment. The gasket  206  is placed in a circular channel  214  formed on the top face of the support  201 , which borders the pumping chamber  205  and on which rests the periphery of the membrane  204 , the latter having a diameter slightly greater than the diameter of the gasket  206 . 
     The membrane  204  is held against the gasket  206  by means of the lid  202 , the latter comprising a bottom face equipped with a raised circular rib  221  having a rounded, convergent bottom edge with a diameter that corresponds to the diameter of the gasket  206  such that said bottom edge of said circular rib  221  presses against the exterior face of the membrane  204  opposite the gasket  206 . 
     The lid  202  extends radially beyond the rib  221  to form a wall  220  successively comprising a second rib  226  and a peripheral skirt  222  that extend coaxially towards the support  201 . The second rib  226  and the peripheral skirt  222  each comprise an annular bottom edge on which is glued the peripheral border of the insulating film  204 A such that water cannot come into contact with the top part of the membrane  204  in case there is a leak around the gasket  206 . 
     According to  FIGS. 7 and 8 , the support  201  comprises three centering tabs  215  disposed at 120° relative to each other and projecting radially to the outside, wherein said centering tabs  215  comprise a curved end between which the periphery of the lid  202  engages in order to ensure the centering of said lid  202  on said support  201 . One of the centering tabs  215  is advantageously wider and engages in a channel  222 A formed at the periphery of the lid  202  for allowing the lid  202  to engage on the support  201  in one direction only. 
     As can be discerned in  FIG. 7 , the angular positioning of the base plate  203  on the support  201  is advantageously achieved by insertion of the centering tabs  215  in corresponding notches  234  on the peripheral rim of the base plate  203 . 
     A silicone film  208  is interposed between the support  201  and the base plate  203 , wherein the positioning of the film  208  on the base plate  203  is ensured by means of cut-outs  280  formed at the periphery of the film  208 , said cut-outs  208  engaging around bosses  230 . 
     The film  208  comprises an arc-shaped cut  282  forming a valve opposite the outlet  212  that opens when water is compressed in the pumping chamber  205  and closes when the piezoelectric actuator  241  bends in the direction for increasing the volume of the pumping chamber  205 . The film  208  also comprises an arc-shaped cut  281  opposite the inlet  211  of the support  201 , forming a valve that closes when the water in the pumping chamber is compressed by the membrane  204 , and that opens when the piezoelectric actuator  241  bends in the direction for increasing the volume of the pumping chamber  205 . 
     The arc-shaped cuts  281  and  282  preferably extend angularly less than 180° and are preferably aligned in the same direction so that a substantial width of material extends between said cuts  281 ,  282 . Such a characteristic makes it possible to achieve good stability of the film  105  in the vicinity of said cuts  281 ,  282  while particularly reducing the risk of the valve bending during the compression of the film between the support  201  and the base plate  203 . 
     In a manner similar to that of the first embodiment of the invention, the support  201 , the lid  202 , and the base plate  203  are held together under stress by means of an elastic clip  209  in the shape of a springy metal strip that engages between the guide ribs  225 ,  235  formed on the periphery of the lid  202  and of the base plate  203 , respectively. 
     The elastic clip  209  has the general shape of a “U”, of which the inwardly curved ends form hooks  291  that hook under the base plate  203 , the clip  209  comprising a center part  290  that applies an axial pressure over an entire center zone  202 A of the lid  202 . 
     According to  FIG. 6 , the center zone  202 A of the lid has a reinforced rigidity so that the pressure exerted by the clip  209  is integrally transmitted via the circular rib  221  to the periphery of the membrane  204  rather than causing the lid  202  to bend. 
     Like the pump shown in the first embodiment, the pump  201  thus configured has the advantage of possessing a membrane  204  the periphery of which is subjected to a substantially constant pressure over time, wherein the elastic clip  209  keeps the lid  202  pressed against the support  201 . Furthermore, the pump according to such an embodiment has the advantage of possessing electrical insulation compliant with the VDE standard in effect in Germany. 
     Obviously the invention is in no way limited to the embodiment described and illustrated herein, which was provided solely by way of an example. Modifications are still possible, particularly in terms of the constitution of the various elements or by substitution of technological equivalents without in any way exceeding the scope of protection of the invention. 
     Hence in a variant of embodiment of the invention, the elastic clip could have a different shape by comprising, for example, four branches spaced at 90° relative to each other. 
     Hence in a variant of embodiment of the invention, the electrical insulation of the piezoelectric element could be achieved by means of an isolation transformer.

Technology Classification (CPC): 5