Abstract:
In an own-medium controlled magnetic valve ( 2 ) actuatable by an electromagnetically controlled pilot vale ( 46 ) for controlling liquids, having a main valve member ( 50 ) in the form of a differential piston and means to suppress pressure surges during the closure of the main valve ( 12 ) implying the cooperation of an overflow channel ( 68, 80, 82 ) with a limited passage cross section between both sides of the main valve member ( 50 ). The overflow channel consists at least partly of an elastic-walled choke channel ( 80 ) which can be increasingly narrowed by squeezing during the closure of the main valve ( 12 ). This ensures that the closing movement takes place rapidly and with enduring precision despite gentle closing.

Description:
BACKGROUND OF THE INVENTION 
     The invention has to do with a magnetic valve, in particular a self-controlling magnetic valve, which is actuated by an electromagnetically controlled initial pilot valve for controlling fluids. The valve has a main valve member in the form of a differential piston and the means to suppress pressure surges when the main valve closes. It includes an overflow channel that has a limited flow-through cross section between both sides of the main valve member, and whose cross section increasingly lessens in the final phase of the closing motion. 
     It has been noticed that cavitation occurs when magnetic valves are closed abruptly, such as in magnetic valves that are used to control water flow in devices like dishwashers and washing machines, particularly those with servocontrol valve functions. This causes noises similar to hammer blows. Additionally, on the inlet side, an impact-like increase in pressure is noted. Efforts have been made to protect against these types of pressure surges by using elastic hoses as inlet and outlet lines. Recently, however, for safety reasons, the magnetic valves in question have been installed directly on the water faucet, and/or linked to the feeding system via lines that are as short as possible and relatively inelastic. For this reason, a proposal has already been made (European Patent No. 0,135,474) to create pressure equalization volumes operating by spring tension, on both the inlet and outlet sides. But such efforts to find a solution are expensive and costly. In addition, with own-medium-controlled magnetic valves, efforts have been made to lessen pressure surges on the inlet and outlet flow sides by giving the overflow channel of the servo valve mechanism a very small cross section, making it possible for the main valve to perform only a delayed closing. However, with this there is a danger that sedimentation and/or dirt particles carried by the controlled fluid will obstruct the channel, and the valve then will no longer be able to close. 
     Additionally, the German Patent Specification No. 976 465 describes an own-medium-controlled magnetic valve according to the generic name. It has an overflow channel that runs vertically through the main valve member, and its cross section is increasingly reduced during motion achieved by having a housing-stable conical pin project into the overflow channel. However, only a quite gradual cross section reduction of an overflow channel, which is relatively narrow even without this, can be achieved, so that the valve closes only after a time lag. Additionally, there is the danger that lime deposits will make the cross section relationships uncontrollable, and/or lead to abrasion of the overflow channel walls. 
     The French Patent Specification No. 1,514,837 offers a self-controlling magnetic valve, also generic, with a rubber elastic membrane that comes into contact on the one hand with the main valve seat, and on the other may be supported radially outside the main valve seat by a ring-shaped fold vis-a-vis the overpressure that acts on it from in the inlet side, under control of a ring-shaped member on a stiff plate surface of the main valve member. The ring-shaped member has, bilaterally, a collar of fine radial grooves, through which a pressure equalization is accomplished between the two sides of the main valve member. Although the flow-through cross section of the flow path so created, may be reduced toward the end of the closing motion with increasing contact pressure on the membrane, it cannot go toward zero, so that the closing still ends in with a relatively impact-type motion. 
     Additionally, the U.S. Pat. No. 2,870,986 offers a magnetic valve that in principle is similar, in which, with increasingly overpressure from the inflow side of the valve, an overflow channel in the main valve member is increasingly restricted in a way that is largely independent of the particular setting of the main valve member, so that the membrane is compressed into an annular groove of a plate-shaped support member. With the “reinforcement member” so created, the valve&#39;s flow rate should be stabilized in relation to the pressure that appears. 
     Here again, as in the other case, a danger exists that the flow-through cross section of the flow path in question can be reduced in the course of time by deposits. 
     SUMMARY OF THE INVENTION 
     Proceeding from this state of the art, the invention has the objective of creating a self-controlling magnetic valve. 
     This takes care to ensure that the closing process takes place while avoiding pressure surges on the inflow and outflow sides, while the valve moves rapidly and with a precision that remains the same over a lengthy period. 
     The overflow channel reduces in cross-sectional size by means of contact pressure of the main valve member on its valve seat. This reduction ensures that the overflow channel reduces in cross section only in the very last phase of the closing motion, but is reduced all the more emphatically. It should be noted that the valve&#39;s flow rate changes in the course of the closing motion with increasing gradients, so that the characteristics of the final phase of the closing motion are of decisive importance. The cross section reduction through the squeezing of the overflow channel that nonetheless depends on the input pressure of the fluid to be regulated, yields, in addition, a control process through which the closing rate of the valve in the critical end phase is largely independent of pressure. However, through mechanical effects of contact pressure by the main valve member on its valve seat, deposits are eliminated as soon as they occur. 
     In a particularly simple way, the choke channel can be configured in the elastic membrane of the main valve member that is customarily present in such valves. This is done in such a way that it can be squeezed together by contact of the membrane on the valve seat that goes with it. Additionally, measures can be taken to bypass the choke channel in question at the beginning of the closing process, and thus accelerate the closing process. 
     For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG.  1 : A perspective drawing of the overall magnetic valve in cross section. 
     FIGS.  2  and  3 : Various perspective drawings of the membrane of the main valve in question. 
     FIGS.  4  and  5 : Various perspective drawings of a membrane insert which is applied in connection with the membrane from FIGS. 2 and 3. 
     FIGS. 6,  7  and  8 : Each show a detail section through the main valve area of the magnetic valve in question in various operational phases, namely, in FIG. 6 with the main valve open. 
     FIG.  7 : toward the end of the closing process of the main valve, and FIG. 8 with the main valve closed. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described with reference to FIGS. 1-8 of the drawings. Identical elements in the various figures are identified by the same reference numerals. 
     The magnetic valve  2  shown has a valve body  4  with an inlet  6  that empties into it from the side, and an outlet  8  that runs downward, i.e., at right angles to inlet  6 . In principle, the exterior section of outlet  8  could also be arrayed to be in alignment with inlet  6 . 
     The inner end of this outlet  8  forms the annular valve seat  10  of main valve  12  (“main valve seat”). Above valve seat  10 , and coaxial with it, a circular-cylindrical recess  14 , open toward the top, is provided in valve body  4 . This recess terminates in a shoulder  16 , on the underside, approximately at the level of valve seat  10 , The shoulder  16  forms a support for a peripheral band  18  of an elastic rubber membrane  20  of main valve  12  which is pressed in sealing fashion by a cylindrical flange  22  of a lid  24  onto shoulder  16 . The lid  24  supports a central, stand-erect core guide pipe  26 , which is surrounded by a hermetically encased magnet coil  28  of an electromagnetic switch system  30 . Magnet coil  28  is contained in a recess  32  of lid  24  that fits it, by means of adjustment and locking devices  34  and  36 . 
     A cylindrical plunger  38  of switch system  30  is supported so that it can glide in core guide pipe  26 . On the upper side, this plunger  38  is subject to the force of a spiral compression spring  42  that acts from the closed end  40  of core guide pipe  26 . The tapered lower end of plunger  38  has an elastic rubber cap  44 , which forms the valve member of a pilot valve  46  for actuating the main valve  12 . Together with membrane  20 , a comparatively stiff membrane insert  48  forms the valve member  50  of the main valve (“main valve member”). 
     As FIGS. 2-5 more exactly show, membrane  20  has a flat bottom  52  with a central shell-shaped piece surrounded by a thin-walled squeeze zone  54 , to which band  18  adjoins on the outside. Floor  52  has a central opening  58 . The membrane insert  48  essentially consists of a shell-shaped part  60  and a so-called top  62 , coaxial with it, in the form of a roughly cross-shaped profiled plug, which adjoins shell-shaped part  60  via a flat base segment that has an annular groove  64 . With the main valve member  50  mounted, the shell-shaped piece  60  comes to lie within the shell shaped piece from floor  52  and squeeze zone  54  of membrane  20 , with the edge that surrounds central opening  58  of the membrane admitted by ring groove  64 . 
     Eccentric to central opening  58 , on a radius smaller than that of valve seat  10  (FIG.  1 ), the bottom  52  of membrane  20  has a perforation  68  bored through, and the membrane insert  48  has a pin  70  that extends loosely through perforation  68 , which pin, relative to perforation  68 , is centered via four ribs  72  arrayed crosswise on it. Additionally, in membrane insert  48 , there is a hole  76  bored through, extending from a central nipple  74  in the interior of its shell-shaped part  60  through the top  62 . Along with the hole  76 , the nipple  74  forms the valve seat of pilot valve  46 . 
     In this regard, the parts of magnetic valve  2  are the usual ones. Their function is the following: 
     If magnet coil  28  is excited, and plunger  38  is consequently drawn against the force of spring  42  into the setting depicted in FIG. 6, pilot valve  46  is opened. Lack of contact pressure on the part of the spring-loaded plunger  38 , and the intrinsic elasticity of membrane  20 , causes the membrane to assume a position removed from valve seat  10 , creating the possibility for fluid located in the so-called pilot valve chamber  78  above membrane  20  to be able to flow away through hole  76  into outlet  8 . In other words, main valve  12  is open. 
     If plunger  38  is released by de-excitation of magnet coil  28 , then its elastic rubber cap  44  closes hole  76 . Thus, the pilot valve  46  is closed. Simultaneously, spring-loaded plunger  38  seeks to press membrane  20  by means of membrane insert  48  downward, against valve seat  10 . This is increasingly supported by the pressure being built up through perforation  68  of the membrane from the inlet side of magnetic valve  2  in the pilot valve chamber  78 . In a normal instance this would result in the main valve member  50  impinging in impact fashion on valve seat  10 , with main valve  12  closing likewise by impact. In contrast, efforts have been made until now, as stated earlier, to sometimes help by having the orifice cross section of an overflow channel, comparable to the perforation  68  of membrane  20 , be designed to be very small. However, this resulted in the danger of its being obstructed unintentionally, as well as of an undesired delay in the closing process. 
     In the present case, however, perforation  68  can be designed to be sufficiently ample that obstruction is all but precluded. Care is taken to avoid a sudden closure of main valve  12  in the following manner: 
     In base  52  of membrane  20 , extending from perforation  68 , a radial choke channel  80  is located. This leads to a perforation  82  displaced radially inward in base  84  of the shell-shaped part  60  of membrane insert  48 . As a result of this, the fluid passing through perforation  68  is forced to pass through choke chamber  80 , in order to reach pilot valve chamber  78 , as long as membrane  20  is in contact with the base of shell-shaped part  60 . 
     Choke chamber  80  is open toward the base  84  of membrane insert  48 . Its wall is elevated over the base of two flat cutouts  86  in base  52  that are ring segment shaped and adjoin it bilaterally, so that it is slightly deformable by resting pressure on the part of membrane insert  48 , in a manner that its cross section in the clear may be reduced to zero. For reasons of symmetry, the two cutouts  86  are supplemented toward the opposite side by two recesses  88  that are likewise ring segment shaped, in order that, with them, they form a collar-shaped arrangement. 
     Two support members in the form of elastically deformable pins  90  project outward from the base of the ring segment shaped cutouts  86  above the remaining base surface. These pins endeavor to keep base  52  of the membrane separated from base  84  of membrane insert  48 . However, they are sufficiently soft to yield to increased pressure on the part of the membrane insert, and thus allow the base  84  of the membrane insert to come into contact with base  52  of the membrane, so that henceforth fluids can get through from perforation  68  of the membrane to perforation  82  of the membrane insert only through choke channel  80 . By this means, an initial reduction of inflow to the pilot valve chamber occurs with increasing pressure buildup as early as in the pilot valve chamber  78 . 
     A further reduction down to zero finally takes place when, with further increasing pressure on the part of the pilot valve chamber  78 , choke channel  80 , which extends over the edge of valve seat  10 , is squeezed together. In this way, inflow to pilot valve chamber  78  becomes increasingly difficult, so that main valve  12  closes smoothly in the final phase. This inflow hindrance is dependent on the amount of the pressure building up in pilot valve chamber  78 . Therefore, the closing action in the final phase is largely independent of pressure. 
     It is noteworthy that the magnet valve  2  that has been described above by way of example differs from previous magnetic valves that lack any special means to reduce pressure surges. It differs in requiring replacement of only two parts, namely the membrane and the membrane insert. In this way, it is also conceivable that previous magnetic valves of this kind could be appropriately retrofitted in a simple manner. 
     There has thus been shown and described a novel magnetic valve which fulfills all the objects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is to be limited only by the claims which follow.