Abstract:
A device for opening or closing a seal seat of a valve arranged in a pipe for liquid or gaseous media includes a one-time only activation of the valve using a shape memory actuator. The shape memory actuator changes its external shape abruptly when a transformation temperature is reached that is dependent upon its alloy composition. The transformation temperature can be generated by a controllable electrical heating device of the device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. §119 to German patent application number 10 2013 012 377.1, filed Jul. 25, 2013, the entire disclosure of which is herein expressly incorporated by reference. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     Exemplary embodiments of the invention relate to a device for opening or closing a seal seat of a valve, which is provided for arrangement in a pipe for liquid or gaseous media. 
     Valves are used, for example, where a pipe for liquid or gaseous media is to be opened or closed. In the closed condition of the valve, a very limited leakage rate must be ensured by the valve. Depending upon the application the valves can be provided for multiple or also only for single actuation, the latter being the case for example in drive systems for space travel applications. 
     In technical systems a distinction is made between Normally Open (NO) and Normally Closed (NC). The designation elates to the switching state before actuation. For example a NO valve is closed upon actuation. 
     In the case of space travel applications high standards are set for the reliability of the activation, since a malfunction can cause substantial damage or even the loss of the drive system. 
     Exemplary embodiments of the present invention are directed to a structurally and/or functionally reliable device for opening or closing a fluid line as well as a corresponding drive system for space travel applications. 
     In a device for opening or closing a seal seat of a valve that is provided for arrangement in a pipe for liquid or gaseous media, according to the invention a shape memory actuator is provided for once-only activation of the valve, the memory actuator changes its external shape abruptly when a transformation temperature is reached which is dependent upon its alloy composition. The transformation temperature can be generated by a controllable electrical heating device of the device. 
     The use of a shape memory actuator enables the once-only and irreversible activation of the valve. The activation takes place by heating the shape memory actuator using the energy supplied from the exterior, i.e. the heating device, so that the actuator changes in size abruptly and as thereby irreversibly changes the current open or closed state of the valve. This operating function can be provided with great reliability. For operation of the valve no further elements are necessary in addition to the shape memory actuator and the heating device, so that the device has a simple mechanical structure. The device can be produced with few components. The device can be provided with a low weight. 
     The valve may comprise a piston disposed in a distribution compartment and which, depending upon whether the valve is opened (NO) or closed (NC) without activation of the shape memory actuator, is or is not pressed by a spring against the seal seat, wherein the shape memory actuator generates a force directed counter to the spring on the piston. 
     The piston can be released from the seal seat or pressed onto the seal seat by the activation of the shape memory actuator depending upon whether the valve is opened or closed without activation of the shape memory actuator. Thus, the piston is moved by the actuation of the shape memory actuator. For this purpose when the transformation temperature is reached the shape memory actuator generates a force which is greater than the force generated by the spring in order to move the piston. 
     The force of the shape memory actuator, i.e. the force applied by the shape memory actuator to the piston, corresponds in the non-activated state to the force generated by the spring. In other words, there is a balance of forces, so that the valve—according to the constructive configuration—is either in the condition NO (normally open) or NC (normally closed). In the non-activated state the shape memory actuator has its so-called “cold” structural state. 
     The movement of the piston is only dependent upon the balance of forces of the spring and the shape memory actuator. This can be achieved, for example, by the spring and the shape memory actuator, lying for example in a common axis, being disposed on opposing sides of the piston. 
     The shape memory actuator may have a spiral shape and the heating device may be disposed in the interior of the spiral shape memory actuator. This enables fast heating of the material of the shape memory actuator in the event of the heating device is activated. A uniform heating of the material of the shape memory alloy is achieved until the transformation temperature is reached. For reasons of redundancy the heating device can also be implemented by a plurality of heating elements. 
     The distribution compartment can be coupled to at least two connections, so that the liquid or gaseous medium can flow through a connection into the distribution compartment and the liquid or gaseous medium can flow through another connection out of the distribution compartment if the valve is opened. 
     The seal seat can be formed by a metal seal, which in the sealed state is pressed against a counterpart. The metal seal can be formed in particular from a ductile material that is plastically deformable when pressed against the counterpart. In this way a low leakage rate can be ensured before actuation for a NC (normally closed) valve or after actuation for a NO (normally open) valve. 
     The heating device can comprise a safety device that deactivates the heating device after the transformation temperature of the shape memory actuator is exceeded. As a result after the operation of the valve damage by the heating device due to excessively high temperatures can be prevented. The switching off of the heating device is also ensured when an activation for a switching element or the switching element for the heating circuit itself are defective. 
     The valve is constructed so that it is rotationally symmetrical with respect to the components that are necessary for the sealing function. This results in a simple and space-saving construction of the device. 
     The valve can comprise three connections and two seal seats, wherein one of the connections is closed by a dummy cap. As a result, depending upon which connection is closed by the dummy cap, a NO (normally open) or NC (normally closed) function can be implemented as required. Such a device can be used flexibly, since at the time of production it is not yet necessary to fix the function (NO or NC). 
     To summarize, in the present invention a valve is activated with a one-way effect shape memory actuator. The shape memory actuator in a suitable configuration changes its external shape abruptly when a transformation temperature dependent upon the alloy composition is reached. The strong forces released in this case are used for the opening and closing of a metal seal seat. The transformation temperature is reached by means of an electrical heating device. The valve can be designed to be actuated once precisely, and in its field of use it is similar to a pyrotechnic valve. 
     Furthermore a drive system for a space travel application is proposed, which has at least one device of the type described above. The drive system has the same advantages as those mentioned in connection with the device described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURE 
       The invention is described in greater detail below with reference to a first embodiment in the drawings. 
         FIG. 1  shows a device according to the invention with a valve, of which the “switching state” can be changed only once by a shape memory actuator. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a device according to the invention with a valve  100 , of which the “switching state” can be changed only once by a shape memory actuator  6 . 
     The valve can be used, for example, in drive systems for space travel applications, for example in order to separate one or more tanks with pressurizing gas from fuel tanks in satellites and space probes. For this purpose the valve  100  must be closed in a non-actuated (activated) state. This state s designated as “normally closed” (NC). The valve can also be used to separate off a fuel supply to a propulsion unit if this is no longer required. For this use the valve must be open in the non-actuated state. This state is designated as “normally open” (NO). The example shown in  FIG. 1  has both the NO (normally open) and the NC (normally closed) functionality. In principle the invention can also be implemented with such a valve  100 , which is designed to allow only one or the other functionality. 
     The device shown in  FIG. 1  consists in principle of two sub-assemblies, namely the valve  100  with two metal seal seats  15 ,  16  and a heating device  8 . The valve  100  has a housing  17  formed rotationally symmetrically around a central axis. The housing  17  has an increased diameter in a central section  18  disposed relative to the longitudinal extent of the central axis. Distribution compartments  2  are disposed in this region and extend around the cylindrical wall of the housing  17 . The device shown in  FIG. 1  can be used as “normally open” (NO), i.e. opened non-actuated or without activation, or “normally closed” (NC), i.e. closed non-actuated or without activation. 
     The decision as to the configuration (NO or NC) in which the device is used can be made after production and takes place by corresponding “wiring” of three connections  3 ,  4  and  5  provided in the embodiment. Each of the connections  3 ,  4 ,  5  is formed in the central section  18  as connecting pieces extending radially in relation to the central axis. The connections  3 ,  4 ,  5  are in each case connected in terms of flow technology to associated distribution compartments  2 . Two of the three connections  3 ,  4 ,  5  are connected to a respective pipe (not shown). 
     If the device is configured as “normally closed” (NC), then, for example, the connection  3  constitutes the outlet and is to be connected to a corresponding outlet pipe. The connection  4  constitutes the inlet and is to be connected to a corresponding inlet pipe. The connecting  5  is connected to a dummy cap (not shown). 
     If the device is to be configured as “normally open” (NO), then for example the connection  5  constitutes the inlet and is to be connected to a corresponding inlet pipe. The connection  3  constitutes the outlet and is to be connected to a corresponding outlet pipe. The connection  4  is connected to a dummy cap (not shown). 
     A piston  12 , which can be moved in the direction of the central axis of the valve  100 , is disposed in the interior of the housing  17  in the region of the central section  18 . The piston  12  consists of two piston plates  12   a ,  12   b  disposed in parallel and are rigidly connected to one another by means of a rod  12   c , which extends in the direction of the central axis of the housing  17 . As a result a volume  21  through which the medium can flow is formed between the piston plates  12   a ,  12   b  when the valve  100  is opened. Each of the piston plates  12   a ,  12   b  has a piston base which face one another and, when the valve  100  is opened, is in contact with the gaseous or liquid fluid. The volume  21  present between the piston bases is dependent upon the length of the rod  12   c  as well as the surface of the piston plates  12   a ,  12   b  or the piston bases. On the side faces of the piston plates  12   a ,  12   b  bordering on the housing  17 , at least one shaft seal  10  is provided in each case completely surrounding the respective piston plate  12   a ,  12   b  and seals the volume relative to spring compartments  19 ,  20  described below. 
     A first spring compartment  19  in which a spring  1  is disposed is formed between the piston  12   a  (i.e. the piston base facing away from the volume  21 ) and the housing  17 . In a corresponding manner a second spring compartment  20  in which a shape memory actuator  6  is disposed is formed between the piston  12   b  (i.e. the piston base facing away from the volume  21 ) and the housing  17 . Thus the piston  12  is disposed in the housing  17  between the spring compartments  19 ,  20 . The spring  1  is disposed in the first spring compartment  19  in such a way that it generates a force acting in the direction of the central axis, the force acting on the piston  21  and attempting to enlarge the volume of the spring compartment  19 . In other words the spring  1  exerts a force acting on the piston  12  in the direction of the second spring compartment  20 . The spring  1  may, for example, be a helical spring. When the shape memory actuator  6  has a cold structural state (i.e. is not “activated”) it exerts an opposing force acting counter to the spring force of the spring  1 . In the non-actuated case, if the shape memory actuator has its cold structural state, the spring  1  and the shape memory actuator  6  are in a balance of forces and the salve piston assumes the position illustrated in  FIG. 1 . 
     In this position the piston plate  12   a  is pressed against the seal seat  15  by the spring force of the spring  1 . The seal seat  15  is formed by a metal seal  11   a , which is based on the plastic deformation of a ductile metal relative to a hard counterpart, and a stop  22  against which the seal  11   a  is pressed. The ductile material of the metal seal  11   a  is disposed as an annular bead on the piston plate  12   a  and is pressed by the spring force of the spring  1  against the stop  22 , which is associated with the piston plate  12   a  and is formed by an annular projection protruding into the volume  21 . As a result the distribution compartment connected to the connection  4  is separated from the volume  21 . 
     A further seal seat  16  is formed by a metal seal  11   b  and a stop  23 . The metal seal  11   b  is disposed as an annular bead on the piston plate  12   b . The stop  23  is associated with the piston plate  12   b  and is formed by an annular projection protruding into the volume  21 . When the seal seat  15  is in the sealing position illustrated in  FIG. 1 , the seal seat  16  is opened, so that the distribution compartment  2  connected to the connection  5  is connected in terms of flow technology to the volume  21 . The metal seals  11   a ,  11   b  enable a limited leakage, based upon the plastic deformation of the ductile metal relative to the hard counterpart, i.e. the stop  22 ,  23 . 
     The movement of the piston  12  is dependent only upon the balance of forces of the spring  1  and the shape memory actuator  6 , but not upon the internal pressure inside the valve  100 . If a suitable electrical voltage is applied to cable ends  14  of the electrical heating device  8 , the temperature of the shape memory actuator  6  rises up to the so-called transition temperature (also designated as the transformation temperature) and the shape memory actuator  6  exerts a force on the piston  12 . The force generated by the shape memory actuator  6  when the trans on temperature is reached is greater than the force applied by the spring  1  to the piston  12 . This force pushes piston  12  to the left until the seal seat  16  seals the volume  21  relative to the distribution compartment  2  connected to the connection  2 . At the same time the seal seat  15  is in a position in which it no longer forms a seal. The transformation temperature is solely dependent upon the alloy composition of the shape memory actuator  6 . 
     An engaging mechanism  9 , which may for example be spring-loaded, ensures that any further movement of the piston  12  is impossible. For this purpose the engaging mechanism has for example spring-loaded pins which are introduced in the region of the side face of the piston plate  12   b  and are moved into corresponding grooves  24  of the housing  17  as soon as the seal seat  16  is reached. In this state a plastic deformation of the seal  11   b  is achieved. 
     When the transformation temperature is exceeded a thermal fuse  7  cuts the current circuit, so that the shape memory actuator  6  is no longer heated by the heating device  8 . 
     In a configuration which is not illustrated the valve can have only two connections and associated distribution compartments. In this configuration even one single seal seat is sufficient. Such a valve may be provided as a NO (normally open) or NC (normally closed) valve. 
     The device described above has a series of advantages and is distinguished in particular from pyrotechnically actuated valves currently in use by the following advantages:
         The device can be more easily dimensioned for different mass flows and pipe cross-sections.   When the valve is actuated small quantities of particles are produced.   The service life of shape memory actuators is not restricted in contrast to pyrotechnic detonators.   The valve opens slowly by comparison with pyrotechnic valves with very small resulting hydraulic shocks.   If the valve is used in a drive system, in particular a space craft drive system, the valve produces no or lower shock loads on the structure of the drive system when the valve is actuated than is the case with conventional pyrotechnically actuated valves.   The valve does not constitute a hazardous material within the meaning of the Explosives Act. Thus no special training (certificate of competence in handling explosives) is necessary for handling thereof.   The electrical activation enables a simpler activation by comparison with pyrotechnic valves.   There are reduced requirements for storage of the components, for example in relation to a temperature range.       

     Thus by the advantages due to its design in contrast to the valves in use nowadays such in space travel applications the valve leads to considerable added value in a drive system, in particular in mission phases which are currently outside the useful life of pyrotechnic valves, for example in scientific missions or end of life. 
     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 
     LIST OF REFERENCE SIGNS 
     
         
           1  spring 
           2  distribution compartment 
           3  input/output 
           4  input/output 
           5  input/output 
           6  shape memory actuator 
           7  (thermal) fuse 
           8  heating device 
           9  engaging mechanism 
           10  shaft seal 
           11   a  seal 
           11   b  seal 
           12  piston 
           12   a  piston plate 
           12   b  piston plate 
           12   c  (piston) rod 
           13  sealing surface 
           14  cable end 
           15  first seal seat 
           16  second seal seat 
           17  housing 
           18  central section 
           19  spring compartment for spring  1   
           20  spring compartment for shape memory actuator  6   
           21  volume 
           22  stop 
           23  stop 
           24  groove 
           100  valve