Abstract:
An undulating diaphragm pump having a propulsion chamber for receiving said diaphragm, wherein the diaphragm has mechanical characteristics that vary from an inlet of the propulsion chamber towards an outlet of the propulsion chamber in such a manner that, when the diaphragm is actuated to deform with a traveling wave that propagates from the inlet towards the outlet of the propulsion chamber in order to propel the fluid, the propagation speed of the wave in the diaphragm in any cross-section relative to the movement of the fluid inside the propulsion chamber is equal to or greater than the mean travel speed of the fluid in said section.

Description:
The invention relates to an improved undulating diaphragm pump. 
     BACKGROUND OF THE INVENTION 
     Pumps are known, e.g. from document FR 2 744 769, that have a diaphragm mounted in a propulsion chamber so as to undulate under drive from at least one linear electromagnetic actuator between two end plates that define a chamber for propelling fluid from an inlet of the pump towards an outlet of the pump. 
     The movable portion of the actuator is generally directly coupled to an outer edge of the diaphragm extending beside the inlet of the propulsion chamber and it imparts transverse oscillation to the outer edge of the diaphragm, thereby causing the diaphragm to undulate perpendicularly to its plane. The effect of coupling between the undulations and the fluid is to propel the fluid from the inlet towards the outlet of the propulsion chamber. 
     In general, the flow section for fluid in the propulsion chamber decreases from the inlet of the propulsion chamber towards the outlet of the pump, thus giving rise, because of flow rate conservation, to an acceleration of the fluid and thus to an increase in the mean speed of the fluid as measured in each cross-section of the propulsion chamber, which speed increases progressively from the inlet towards the outlet of the propulsion chamber. 
     OBJECT OF THE INVENTION 
     The invention seeks to propose a diaphragm pump that makes greater efficiency possible. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In order to achieve this object, the invention provides an undulating diaphragm pump having a propulsion chamber for receiving said diaphragm, the diaphragm having mechanical characteristics that vary from an inlet of the propulsion chamber towards an outlet of the propulsion chamber in such a manner that when the diaphragm is actuated to deform with a traveling wave that propagates from the inlet towards the outlet of the propulsion chamber in order to propel the fluid, the propagation speed of the wave in the diaphragm in any cross-section relative to the movement of the fluid inside the propulsion chamber is equal to or greater than the mean travel speed of the fluid in said section. 
     This ensures that the diaphragm wave advances at all points in the propulsion chamber at a speed that is faster than that of the fluid it is propelling, and that the diaphragm transmits its mechanical energy to the fluid over the entire propagation length of the wave along the diaphragm. The coupling between the undulating diaphragm and the fluid is thus optimized, with the movement of the diaphragm being more efficient, since the entire surface area of the diaphragm is propulsive, thereby improving the efficiency of the pump. 
     It is thus possible to increase the speed of the fluid at the outlet from the propulsion chamber and to obtain relatively large flow rates, making it possible to decrease the diameter of the diaphragm and the overall size of the pump head. In addition, this makes it possible to avoid any positive transfer of energy from the fluid to the diaphragm which would run the risk of causing the diaphragm to come into contact with the end plates. Such contacts give rise to noise and run the risk of damaging the diaphragm. It is also possible to reduce the pulsations in the pressure and in the flow rate at the outlet from the propulsion chamber. 
     In a particular embodiment of the invention, the diaphragm has imparted thereto stiffness that varies and that increases going from the inlet towards the outlet of the propulsion chamber. It is known that stiffness is an important parameter for determining the propagation speed of the traveling wave that deforms the diaphragm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood in the light of the accompanying drawings, in which: 
         FIG. 1  is a diagrammatic half-view in section of an undulating diaphragm pump of the invention; 
         FIGS. 2A ,  2 B,  2 C, and  2 D are partially cut-away perspective views of a disk-shaped diaphragm in various particular embodiments of the invention; 
         FIG. 3  is a section view of an undulating diaphragm pump fitted with a diaphragm having a neck in another particular embodiment of the invention; and 
         FIGS. 4 ,  5 ,  6 ,  7 , and  8  are perspective views of diaphragms in other particular embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , the undulating diaphragm pump of the invention comprises a diaphragm that extends between two end plates  2  that constitute a fluid propulsion chamber. An actuator (not shown) is connected to an edge  3  of the diaphragm and actuates the edge  3  of the diaphragm transversely so as to cause the diaphragm to undulate with a traveling wave that propagates from the edge  3  towards the center  4  of the diaphragm. Fluid is thus transferred between the two end plates from an inlet of the propulsion chamber at the periphery thereof towards an outlet of the propulsion chamber situated at the center thereof. 
     If Z is the axis of revolution of the pump, and if the pump is notionally sectioned on a circular cylinder about the axis Z, it can be seen that the portion of the cylinder that is situated between the end plates  2  defines a working section for passing the fluid, ignoring the section of the diaphragm intersected by the cylinder. Naturally, on coming closer to the center of the diaphragm, the area of the working section decreases because of the decrease in the radius of the cylinder, and also because the two end plates come closer together. For an incompressible fluid such as a liquid, the law of flow rate conservation between the inlet and the outlet of the propulsion chamber causes the mean flow speed of the fluid through the various working sections to increase in proportion to the decrease in the area of the working section. 
     The invention seeks to propose a diaphragm that takes account of this variation in the mean speed of the fluid between the inlet and the outlet of the fluid propulsion chamber. 
     With reference to  FIG. 1 , the fluid flow sections lie between the diaphragm and the end plates, and the crests of the waves form constrictions in section that advance at the propagation speed of the wave. The pressure difference between the pressure P 1  upstream from a constriction and the pressure P 2  downstream from the constriction depends on the speed difference between the propagation speed of the wave and the mean speed of the fluid. The product of this pressure difference (P 1 −P 2 ) multiplied by the mean flow rate in said section corresponds to the hydraulic power that is locally transmitted to the fluid. 
     Maintaining a positive speed difference throughout the cross-section of the propulsion chamber makes it possible to guarantee positive power transmission to the fluid over the entire propagation length of the wave along the diaphragm, i.e. over the entire active radius of the diaphragm in this example. 
     Thus, wave conditions establish a series of constrictions and pressure differences that extend from the inlet pressure to the outlet pressure of the propulsion chamber. The difference between the inlet pressure and the outlet pressure multiplied by the mean flow rate corresponds to the mean hydraulic power transmitted to the fluid. In this example it is ensured that the diaphragm transmits its mechanical energy to the fluid over its entire active radius, with a traveling wave in the diaphragm propagating throughout the cross-section of the propulsion chamber at a speed that is faster than the speed with which the fluid travels through said section of the propulsion chamber. 
     In the particular embodiment given reference A in  FIG. 2 , the diaphragm  1  is made up for this purpose of concentric annular portions that are made of materials that have different moduluses of elasticity and that are disposed in such a manner that the modulus of elasticity E of the material of the diaphragm increases from the peripheral edge  3  of the diaphragm going towards the center  4  of the diaphragm more quickly than the thickness h of the diaphragm decreases. The variation in the modulus of elasticity E is represented symbolically by a succession of annular zones, naturally constituted in the detail view solely by their sections in the section plane. Thus, the product Exh measured in a cross-section increases continuously going from the edge  3  towards the center  4  so that the propagation speed of the traveling wave that deforms the diaphragm  1  in operation increases continuously. 
     In  FIG. 2 , it can be seen that the cylinder of radius R 1  defines a working flow section S 1  (of circular cylindrical shape) for the fluid and that the cylinder of radius R 2  defines a working flow section S 2  (likewise of circularly cylindrical shape) for the fluid, the areas of these two sections being in the ratio (R 2 /R 1 ) 2 ×h 2 /h 1 , where h 1  and h 2  are the heights between the end plates at the sections S 1  and S 2  respectively. The area of the section S 2  is thus considerably smaller than the area of the section S 1 , and the speed of the fluid in the section S 2  is thus greater than the speed of the fluid in the section S 1 . 
     It is appropriate to ensure that the variation in the product Exh, which is one of the important parameters determining the propagation speed of the traveling wave that deforms the diaphragm, varies sufficiently quickly to ensure that the propagation speed is always higher than the mean speed of the fluid, or indeed increases faster than the speed of the fluid on approaching the center of the propulsion chamber. 
     If this condition is satisfied, then the diaphragm transmits its mechanical energy to the fluid over the entire propagation length of the wave along the diaphragm, i.e. along the entire active radius of the diaphragm. 
     With reference to the embodiment referenced B, the diaphragm  11  is made out of two materials: a core  12  out of a material having a large modulus of elasticity E 1  and of thickness h 1  that is constant or that increases as shown going from the edge  13  towards the center  14 , and a covering  15  that extends on either side of the core  12  and that is made of a material having a lower modulus of elasticity E 2  and of thickness 2×h 2  that decreases from the edge  13  towards the center  14 . The assembly is made in such a manner that the quantity
 
E1×h1+E2×2×h2
 
increases from the edge  13  towards the center  14  sufficiently to impart a propagation speed to the traveling wave that deforms the diaphragm  12  such that the propagation speed increases more quickly than the decrease in the working section for fluid flow. With reference to the embodiment referenced C, the diaphragm  21  is constituted by a material that is homogeneous. It is cut into the shape of a disk of thickness h that is generally decreasing from the edge towards the center, and in which annular grooves are formed at intervals that are regular in this example so as to leave a core that is of thickness that is constant in this example. The density of the material is written ρ and the density per unit area of the diaphragm is equal to the product ρ×h, with the grooves being arranged in such a manner that the mean of the quantity ρ×h over a distance  d  including a trough and a ridge decreases on approaching the center, such that this technical configuration also gives rise to progressive variation in the propagation speed of the wave.
 
     With reference to another embodiment referenced D, the diaphragm  31  comprises a core  32  made of a material having a large modulus of elasticity E 1  and a constant thickness h 1 , together with a covering  35  made of a material having a small modulus of elasticity E 2  and presenting annular grooves as in the above-described embodiment. 
     In yet another embodiment, as shown in  FIG. 3 , the diaphragm  41  includes a neck  45  at its center, the neck extending along the axis Z into the delivery duct  46  at the outlet from the propulsion chamber. The neck  45  forms a stiffener that contributes to increasing the stiffness of the diaphragm towards its center  44 , such that the propagation speed of the traveling wave increases. 
     In addition, the neck  45  offsets the point where the fluid flows on either side of the diaphragm  41  join together to outside the propulsion chamber, and it makes use of the dynamic pressure of the fluid at the outlet from the neck so as to conserve a pressure differential between the faces of the diaphragm in its central portion inside the propulsion chamber. The central portion of the diaphragm thus works under better conditions, and the efficiency of the pump is thus improved. 
     In  FIG. 5 , the diaphragm  71  comprises a core  72  made of a material having a large modulus of elasticity and presenting in the vicinity of its edge  73  a peripheral zone  75  that is made more flexible by having a profile in the form of wavelets  76  that make the diaphragm  71  more flexible in the vicinity of its edge  73 . 
     In  FIG. 6 , the core  72  is embedded in a layer  76  of flexible material that forms a covering. 
     In the embodiment of  FIG. 7 , the diaphragm  71  comprises a core  72  made of a material having a large modulus of elasticity that is provided in the vicinity of its edge  73  with a flexible peripheral zone  75  presenting a profile of crenellations  77  imparting flexibility to the vicinity of the edge  73 . 
     As can be understood from the above, the above-described embodiments relate to diaphragms forming bodies of revolution and having mechanical characteristics that are constant along any circle centered on the central axis Z, even though those characteristics vary radially going from the edge towards the center. 
     Nevertheless, it is possible while remaining within the ambit of the invention, to provide diaphragms in which the mechanical characteristics vary radially, but are not necessarily constant around a circle. Thus, as in the embodiment shown in  FIG. 4 , the diaphragm  51  may be made in composite manner with a star-shaped stiffener  52  made of a material having a large modulus of elasticity, comprising a central ring from which branches project. The stiffener  52  is incorporated in a web  55  made of a material having a small modulus of elasticity. In the same manner as described above, this type of diaphragm enables a traveling wave starting from the edge  53  and going towards the center  54  to propagate at a speed that increases. 
     In the embodiment of  FIG. 8 , the diaphragm  61  comprises a core  62  carrying ribs  65  that extend radially from the center  64  of the diaphragm  61  towards the edge  63  as far as a middle portion of the diaphragm  61  between the center  64  and the edge  63 . The ribs  65  are of decreasing height such that the ribs  65  present a maximum height close to the center  64  and zero height in the middle portion. 
     The core  62  is made of a material that is relatively flexible and that is stiffened progressively by the ribs  65  going towards the center  64 . 
     The core  62  may optionally be covered by a covering so that the diaphragm presents faces that are plane. 
     The invention is not limited to the description above, but on the contrary covers any variant coming within the ambit defined by the claims. 
     In particular, although the invention is described with reference to diaphragms that are disk-shaped, it is clear that the invention applies equally well to diaphragms that are strip-shaped or that are tubular. It should be observed that in pumps that use diaphragms of this type, the working section for fluid flow through the propulsion chamber decreases only because the two end plates come closer together and possibly also because the diaphragm becomes thicker, but at a rate that is slower than in pumps having disk-shaped diaphragms of the kind described above. The variation in speed between the inlet and the outlet of the propulsion chamber is thus less marked. As a result, the variation in the mechanical characteristics of the diaphragm for causing the propagation speed of the wave in the diaphragm at all cross-sections relative to fluid flow inside the propulsion chamber to be equal to or greater than the travel speed of the fluid in said section takes place more slowly and it is therefore easier to implement. 
     In a variant, the modulus of elasticity E of the diaphragm may vary more slowly than the thickness of the diaphragm decreases, but the performance of the pump will nevertheless be diminished compared with the embodiment described. 
     In a variant, diaphragm may be made of a single material that is treated locally so as to obtain variation in its modulus of elasticity (the treatment may be hot deformation, particle bombardment, local doping, . . . ).