Abstract:
A multiway valve contains a housing having several inlets and outlets and a chamber. Several seats are provided and each is respectively associated with one inlet or one outlet. A closure element is provided which can move between the seats and at least one actuator is provided in the form of an element made of a form memory alloy, able to displace the closure element from one of the seats when heating occurs. A spring element presses the closure element against each respective seat that it engages.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a continuation, under 35 U.S.C. § 120, of copending international application No. PCT/EP02/14175, filed Dec. 12, 2002, which designated the United States; this application also claims the priority, under 35 U.S.C. § 119, of German patent application No. 101 62 498.0, filed Dec. 19, 2001; the prior applications are herewith incorporated by reference in their entirety. 

   BACKGROUND OF THE INVENTION 
   Field of the Invention 
   The present invention relates to a multiway valve and to a refrigerating machine in the circuit of which such a multiway valve is inserted. 
   Such multiway valves or refrigerating machines are used, for example, in refrigerators that have a plurality of cooling compartments capable of being regulated in each case by a specific evaporator to temperatures which can be set independently of one another; they serve there for apportioning the refrigerant stream to one or more evaporators. The multiway valves used at the present time in refrigerating machines are generally solenoid valves. These have a housing with a plurality of valve seats and with a closing member movable between stable positions, in each case on one of the valve seats, by a magnetic force. 
   A solenoid valve, not actuated magnetically, is known from Published, Non-Prosecuted German Patent Application DE 198 22 735 A1. The housing of the known multiway valve contains three chambers, including a middle chamber, in which a closing member is movable between two seats on opposite side walls, and two lateral chambers, into which the orifices of the valve seats issue and in which a spring formed of a form memory alloy is accommodated in each case. The two springs press onto the closing member in the middle chamber in each case via a piston and a rod extending through the orifice of the respective valve seat. By a first of the two lateral chambers being heated, the spring located in it is lengthened and presses the closing member against the valve seat leading to the second lateral chamber, at the same time compressing the spring in the second lateral chamber. 
   The adjusting movement of the closing member between the two mutually opposite valve seats is, in this known multiway valve, driven solely by the springs formed of form memory alloy. For this purpose, the spring has to be capable of generating considerable stroke which will generally be greater than the distance between the two valve seats, since, in order to release the closing member from a seat, the spring disposed in the chamber lying behind it must first build up the necessary pressure in order to overcome a pressure difference possibly applied to the initially still closed valve seat and, finally, to press the closing member against the opposite seat with a spring force which does not disappear. Moreover, the resistance of the spring in the opposite lateral chamber has to be overcome. 
   So that the closing member can be pressed with a predetermined force against the valve seat of the opposite chamber, the spring must be configured in such a way that, when the closing member bears against the opposite valve seat, the spring is shorter by the amount of a displacement distance δL than in its free relaxed state. The displacement distance δL is smaller than the length difference ΔL of the spring between the compressed state and the free relaxed state. The fatigue phenomena of the spring, which may occur in the case of long-term use, may lead to a reduction in the length of the spring in the free relaxed state, with the result that δL becomes zero or even negative and the stroke necessary for displacing the closing member toward the opposite valve seat can no longer be applied. 
   SUMMARY OF THE INVENTION 
   It is accordingly an object of the invention to provide a multiway valve which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which can be changed over with the aid of an element formed of a form memory alloy and where the closing member of the multiway valve is pressed reproducibly, with a constant force independent of fatigue phenomena of an element formed of form memory alloy, against the valve seat occupied in each case. 
   With the foregoing and other objects in view there is provided, in accordance with the invention, a multiway valve. The multiway valve contains a housing having a plurality of inlets and outlets and at least one common chamber. A plurality of seats are provided and each is associated with one of the inlets or outlets. A closing member is movable between the seats and is disposed in the housing. At least one actuator being an element formed of a form memory alloy, is provided. The element is capable, under heating, to displace the closing member onto one of the seats. A spring element is provided for pressing the closing member against each of the seats occupied by the closing member in each case. 
   The spring element independent of an actuator may be produced from any desired spring-elastic material with better long-term stability than that of the form memory alloy. Materials of this kind, in particular spring steels, are available to a person skilled in the art. During the changeover of the multiway valve according to the invention, when the closing member is displaced from a seat, an actuator initially acts counter to the resistance of the spring element. Finally, in this case, a point of equilibrium is exceeded, from which the force of the spring element begins to press the closing member against another seat. From this point of equilibrium, therefore, the spring element assumes the drive of the movement of the closing member, and the force with which the closing member is pressed against the respective valve seat is applied by the spring element. How great is the force which the actuator formed of form memory alloy is still capable of exerting on the closing member at the point of equilibrium and how far the actuator is deformed until it reaches a position of rest are unimportant for the functioning capacity of the valve according to the invention. This force can therefore be dimensioned generously on a new valve, so that it is certain that it does not become zero due to fatigue. 
   The spring element used is preferably a leaf spring. 
   As a result of a preferred refinement of the invention, the closing member is movable between two seats facing one another, and the leaf spring is capable of assuming two stable positions, a convex curvature of the leaf spring facing one of the seats in each of the positions. 
   The actuator used is preferably a curved body with a convex side facing the closing member, the body being lengthened under heating. Such heating leads, in the case of retained ends of the body, to an increase in curvature and consequently to a movement of the convex side in the direction of the closing member, as a result of which the closing member can be displaced from its seat. The curved body may have, in particular, a plate or beam shape. 
   According to a preferred refinement, the multiway valve has a housing with a central chamber, in which the closing member is movable, and at least one peripheral chamber. Each peripheral chamber receives an actuator and is capable of communicating with the central chamber via an orifice surrounded by one of the seats. A transmission pin for transmitting a deformation of the actuator to the closing member extends through the orifice. 
   In an alternative refinement, the spring element and the at least one actuator are accommodated in a common chamber. In this case, the actuator is expediently disposed between a sidewall of the housing and the spring element, the sidewall having located in it that seat from which the actuator can displace the closing member. 
   In this refinement, the actuator preferably has an orifice through which the closing member can be moved in order to close or open the seat. 
   For the selective heating of each actuator, the latter is in each case assigned an electrical heating device. The heating device is preferably a heating resistor that extends on the surface of the actuator. The configuration makes it possible to bring the heating device into direct contact with fluid which flows through the valve and thus to cool the actuator quickly again after its actuation. This is expedient so that the multiway valve can be operated with high switching frequency. 
   It is simpler and more cost-effective to dispose a heating device outside the housing than to dispose a heating device on the surface of the actuator. So that, in this refinement, too, a rapid heating of an actuator can be achieved, it is expedient for the housing of the multiway valve and the actuator to be constructed in one piece from a form memory alloy, in order thereby to minimize heat transmission resistances between the housing part heated by the heating device and the actuator. 
   The subject of the invention is, furthermore, a refrigerating machine with a refrigerant circuit having a plurality of evaporators, in which refrigerating machine a multiway valve of the above-defined type for apportioning refrigerant to the various evaporators is disposed in the refrigerant circuit of the machine. 
   Other features which are considered as characteristic for the invention are set forth in the appended claims. 
   Although the invention is illustrated and described herein as embodied in a multiway valve, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
   The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagrammatic, perspective view of a first embodiment of a multiway valve according to the invention; 
       FIG. 2  is a diagrammatic, sectional view through the multiway valve of  FIG. 1  taken along the plane defined by lines A, B in  FIG. 1 ; 
       FIG. 3  is a diagrammatic, sectional view taken along the plane defined by lines A, C in  FIG. 1 ; 
       FIG. 4  is a diagrammatic, perspective, partially cutaway view of a second embodiment of the multiway valve according to the invention; 
       FIG. 5  is a diagrammatic, sectional view through a third embodiment of the multiway valve; 
       FIG. 6  is a diagrammatic, axial section view through the multiway valve according to the invention with three outlets; and 
       FIG. 7  is a diagrammatic, sectional view through the multiway valve of  FIG. 6  perpendicularly to its axis. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown a multiway valve according to the invention with a housing  1  formed of metal, which on one housing side, here the top side facing away from the viewer, has an inlet connection  2  and, on an opposite housing underside  3 , two outlet connections  4   a ,  4   b  for a fluid. Two current leadthroughs  18  are likewise led on the underside  3  into an interior of the housing  1  so as to be insulated relative to the latter. A ground connection is connected directly to the housing at any desired point and is not illustrated in  FIG. 1 . 
     FIG. 2  shows a “horizontal” section through the multiway valve of  FIG. 1  in the plane defined by the lines A, B of  FIG. 1 . A slide  6  formed of an electrically nonconductive material, for example plastic, is mounted displaceably in the direction of the line A in a chamber  5  inside the housing  1 . The slide  6  contains a base plate  8  guided displaceably on a side wall  7  of the housing  1  and two legs  9   a ,  9   b  which, starting from the base plate  8 , extend as far as a short distance from the opposite side wall  10  of the housing. The legs  9   a ,  9   b  subdivide the chamber  5  into a central chamber  11  between the two legs  9   a ,  9   b  and two lateral chambers  12   a ,  12   b  in each case on the far side of the legs  9   a ,  9   b.    
   A ball  13  functioning as a closing member is accommodated in the central chamber  11 . In the configuration of the multiway valve, as shown in  FIG. 2 , the ball  13  lies centrally on a left valve seat  14   a  formed on the bottom of the chamber  5  and thus shuts off the outlet connection  4   a  assigned to the valve seat  14   a  (see also  FIG. 3 ). A second right valve seat  14   b , which belongs to the right outlet connection  4   b , is open. 
   The two lateral chambers  12   a ,  12   b  accommodate elements  15   a ,  15   b  which are formed of a form memory alloy, here in the form of curved bars, and which are in each case held at one end on the housing  1 . A second end of the left element  15   a  is in bearing contact in a recess  20   a  on the left leg  9   a , and a corresponding second end of the right element  15   b  lies opposite such a recess  20   b , without reaching it. The element  15   b , which is in the memory configuration corresponding to a hot state, is thus fully relaxed. However, the memory configuration can also be selected such that the end of the element  15   b  just reaches the clearance  20   b  or presses against the latter with a slight residual force. Around each element  15   a ,  15   b  is wound a resistance wire  16  which is connected, at its end facing the leg  9   a  or  9   b , to a conductor  17  of one of the leadthroughs  18  and the opposite end of which is connected to ground via the housing  1 . 
     FIG. 3  shows a section through the multiway valve of  FIG. 1  in the plane defined by the lines A, C in  FIG. 1 . A height of the slide  6  is smaller than the diameter of the ball  13 , and a leaf spring  19  clamped above the slide  6  between the ball  13  and the top side of the housing  1  exerts on the ball  13  a downwardly directed force which keeps the ball  13  pressed firmly against the seat occupied in each case by it, here the seat  14   a.    
   When the element  15   a  is heated with the aid of its resistance wire  16 , it stretches out and at the same time displaces the slide  6  to the right. In this case, the left leg  9   a  displaces the ball  13  from its place on the left valve seat  14   a . During the displacement, the ball  13  is lifted, counter to the downwardly directed force exerted by the leaf spring  19 , until it assumes an unstable position of equilibrium between the two valve seats  14   a ,  14   b . When the ball  13  has overcome this position of equilibrium, the force of the leaf spring  19  drives it in the direction of the right valve seat  14   b , and, as a result of the movement of the ball  13 , the slide  6  is released from the element  15   a  and driven along. The element  15   a , which then no longer has any work to perform, can stretch out further, until it assumes the configuration of equilibrium corresponding to its hot state. When the slide  6  butts with its clearance  20   b  onto the element  15   b , it deforms the latter, driven by the force of the leaf spring  19 , until the ball has reached the right valve seat  14   b . Since the element  15   b  is cold, the force to be applied for this deformation is substantially lower than the force that the heated element  15   a  applied in order to displace the ball  13  as far as the point of equilibrium. 
   The force with which the ball  13  is pressed against the valve seat  14   b  is determined by the force of the spring  19  and, if appropriate, by a pressure falling at the valve seat. It is independent of the exact value of the force supplied by the element  15   a . Fatigue or other drift in the behavior of the element  15   a  therefore has no effect on the closing force acting on the ball  13 , as long as the force of the element  15   a  is sufficient to force the ball  13  beyond the position of equilibrium. 
     FIG. 4  shows a perspective view of the multiway valve according to a second embodiment of the invention, with a cutaway housing  1 . The closing member  13  is movable in the chamber  5  of the housing between the two valve seats  14   a ,  14   b  which belong to the two outlet connections  4   a  and  4   b  disposed opposite one another on an underside and a topside of the housing  1  respectively. The closing member  13  is essentially in the form of a cylinder with rounded end faces. The closing member  13  is fastened in a central passage of the leaf spring  19  via a peripheral bead  22  which is clamped between the top side of the leaf spring  19  and a holding ring  23  fastened to the leaf spring  19 , for example by spot welding. The leaf spring  19  extends over the entire length of the chamber  5  and is held at two ends in grooves  21  which extend over two narrow sides of the chamber  5  which are located opposite one another. 
     FIG. 4  shows the leaf spring  19  in an upwardly curved state, that is to say the convex side of the leaf spring  19  faces the valve seat  14   b  on the top side of the housing  1 , and the leaf spring  19  presses the closing member  13  against the seat  14   b  in order to close the latter. 
   Two plate-shaped elements  15   a ,  15   b  formed of form memory alloy are disposed in the chamber  5  in each case above and below the leaf spring  19  and, like the latter, are held in grooves  21  on the narrow sides of the chamber. The elements  15   a ,  15   b  in each case have a central orifice  24   a ,  24   b , through which the closing member  13  can engage in order to close the valve seat  14   a  or  14   b  assigned to the element  15   a  or  15   b.    
   A resistance wire  16  extends in a zigzag over the surfaces of the elements  15   a ,  15   b . It may extend over the topside and the underside of each element  15   a ,  15   b  or over only one of the two sides in each case. The resistance wire  16  of each element  15   a ,  15   b  can be acted upon by current independently of the other element  15   b ,  15   a , in order to heat the respective element selectively. 
   When, in the configuration shown in  FIG. 4 , the resistance wire  16  of the upper element  15   b  is supplied with current, the element  15   b  is lengthened, and, since it is held at its longitudinal ends in the grooves  21 , the lengthening has the result that the central element region surrounding the orifice  24   b  moves downward and presses the leaf spring  19  downward. The leaf spring  19  thereby comes increasingly under tension, and, as soon as a point of equilibrium at mid-height of the chamber  5  is overcome, the leaf spring  19  moves abruptly downward, at the same time deforming the lower element  15   a , and the closing member  13  impinges onto the seat  14   a  and closes the latter. As soon as, after the changeover of the valve has taken place, the supply of heating current to the element  15   b  is discontinued, the latter cools rapidly in the stream of fluid flowing from the inlet connection  2  through the chamber  5  to the outlet connection  4   b . The element  15   a  can then be supplied with heating current, and the operation described above takes place in the opposite direction. 
     FIG. 5  shows a third embodiment of the valve according to the invention in section. The housing  1  is assembled, here, from a plurality of parts, a central frame  30 , two intermediate walls  31   a ,  31   b  and two side parts  32   a ,  32   b . The frame  30  and the two intermediate walls  31   a ,  31   b  delimit a central chamber  11  of the valve, in which the closing member  13 , spherical again here, is held on the leaf spring  19 . As in the example of  FIG. 4 , the leaf spring  19  has two stable states, in each case with an opposite curvature, in which it presses the closing member  13  in each case against one of two valve seats  14   a ,  14   b  which, lying opposite one another, are disposed in the intermediate walls  31   a ,  31   b.    
   The intermediate walls  31   a ,  31   b , together with the side parts  32   a ,  32   b , delimit in each case lateral chambers  12   a ,  12   b  of the multiway valve in which an element  15   a ,  15   b  formed of form memory alloy extends. As in the example of  FIG. 4 , the elements  15   a ,  15   b  are in the form of rectangular plates, two opposite edges of which are clamped on walls of the lateral chambers  12   a ,  12   b  in such a way that the elements  15   a ,  15   b  have a curvature with the convex side facing the closing member  13 . A heating resistor  16  is applied to the front and the rear side of the elements  15   a  and  15   b.    
   Two transmission pins  33   a ,  33   b  extend through orifices, surrounded by the valve seats  14   a ,  14   b , of the intermediate walls  31   a ,  31   b  between the elements  15   a  and  15   b  and the closing member  13 . 
     FIG. 5  shows the leaf spring  19  in a state curved to the left, in which it keeps the closing member  13  pressed against the left valve seat  14   a . When, in this configuration of the valve, the left element  15   a  is heated and therefore increases its length, this leads to an increase in its curvature, so that the closing member  13  is displaced from the seat  14   a  via the transmission pin  33   a . After passing through the position of equilibrium in the middle of the central chamber  11 , the curvature of the leaf spring  19  tips to the right, as a result of which the element  15   b  in the right lateral chamber  12   b  is compressed via the transmission pin  33   b  and the closing member  13  shuts off the seat  14   b.    
   The resistance wires  16  of the two elements  15   a ,  15   b  are supplied jointly with heating current via two connections  35   a ,  35   b.    
   The connection  15   a  is connected to a first current leadthrough  18  of the left lateral chamber  12   a  via a first diode  36   a  and to a first current leadthrough  18  of the right lateral chamber  12   b  directly. The connection  35   b  is connected to a second current leadthrough  18  of the left lateral chamber  12   a  directly and to a second current leadthrough  18  of the right lateral chamber  12   b  via a second diode  36   b . The diodes  36   a ,  36   b  are connected antiparallel, so that, depending on the sign, a heating current applied to the connections  35   a ,  35   b  supplies only the resistance wire  16  of the element  15   a  or that of the element  15   b.    
   The valves according to  FIGS. 1 to 3  and  4  may, of course, also be supplied with current via antiparallel diodes  36   a ,  36   b.    
   A fourth embodiment of the invention is described with reference to  FIGS. 6 and 7 . The multiway valve according to the fourth embodiment has a cylindrical housing  1  which is shown in a section along the axis in  FIG. 6  and in a section transversely to the axis in  FIG. 7 . 
   The housing has three outlet connections  4   a ,  4   b ,  4   c  which are disposed in each case at intervals of 120° about the axis. An inlet connection  2  may be placed at essentially any desired point on the housing  1 . A beam-shaped spring element  40  is held by an upper and lower wall  41  of the housing in each case at the intersection points of the walls  41  with the longitudinal axis. The spring element  40  is longer than the chamber  5  delimited by the walls  41  and runs, curved, through the chamber  5 . Fastened central to the spring element  40  is a spherical closing member  13  that, in the position shown in the  FIGS. 6 and 7 , shuts off the valve seat  14   c  of the outlet connection  4   c.    
   Strip-shaped elements  15   a ,  15   b ,  15   c  formed of form memory alloy are disposed in each case between two outlet connections at an angular interval of 60° of these in the chamber  5 . The element  15   c  located opposite the outlet connection  4   c  is shown in an elongated state engaging into the interior of the chamber  5 ; the elements  15   a ,  15   b  adjacent to the outlet connection  4   c  are compressed, so that they do not obstruct the access of the closing member  14  to the valve seat  14   c . When one of the compressed elements, for example the element  15   a , is heated with the aid of a heating resistor, not illustrated, attached to its surface, it begins to curve toward the axis of the housing and at the same time to displace the closing member  13  from the valve seat  14   c  counter to the resistance of the spring element  40  and push it toward the surface of the element  15   b . In order in this case to prevent an excessive compression of the element  15   b , the rear side of the latter has disposed on it a supporting body  42   b  that prevents the element  15   b  from being compressed beyond its position shown. As soon as the element  15   a  has displaced the closing member over more than half the excursion toward the valve seat  14   a  located opposite it counter to the force of the spring element  40 , the spring element  40  begins to assist the further movement of the closing body  13  and pushes the latter against the seat  14   a , at the same time compressing the element  15   c . Each of the three elements  15   a ,  15   b ,  15   c  is thus capable of displacing the closing member  13  from the two valve seats adjacent to it and of closing the opposite valve seat. 
   Multiway valves of the type described above can be used particularly advantageously in refrigerating machines for refrigerators that have a plurality of evaporators for cooling compartments to be regulated separately, where they can be used for distributing a refrigerant stream to the various evaporators. In such a refrigerating machine, when one of the elements formed of form memory alloys is heated, refrigerant surrounding it will generally begin to boil, this resulting, in the first place, in a good thermal insulation of the element with respect to its surroundings. As soon as the element is no longer supplied with heating current, the evaporated refrigerant surrounding it is entrained by the stream flowing through the valve, so that the element comes into contact with liquid refrigerant and is rapidly cooled again. As soon as the element has cooled, a new switching operation is possible.