Abstract:
A valve ( 1 ) with a AND gate function has a valve member ( 2 ) cooperating with moving passage members ( 23   a  and  23   b ) in a valve housing ( 3 ) in order to control connections between one outlet (A) and two inlets (E 1  and E 2 ). If the pressure difference present at the input side goes above a threshold value, the valve member ( 2 ) can thrust back one of the passage members ( 23   a  and  23   b ) against the stressing force of the stressing means ( 34   a  and  34   b ) in order to separate the outlet (A) simultaneously from both inlets (E 1  and E 2 ). Accordingly a safety and/or a logic function may be implemented.

Description:
This application claims priority based on an International Application filed under the Patent Cooperation Treaty, PCT/EP2007/005821, filed Jun. 30, 2007. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a valve with an AND gate function in the case of which a valve member able to be shifted in relation to a valve housing controls the fluid connection between two inlets and an outlet, its switching position being dependent on the pressure difference between the fluid pressure obtaining at the two inlets so that at equal input pressures at least one inlet is joined with the outlet, and the valve member can assume two opposite terminal positions in which it clears one of two first passages stationary arranged in the housing and connected with the outlet and simultaneously shuts off the other first passage. 
     A valve having these features is disclosed in the product catalog entitled “Der Pneumatic-Katalog 97/98”, issue of 97/98, thirty-third edition, Festo AG &amp; Co., page 11.5/10-2. This valve possesses one outlet and two inlets, the outlet always being subject to pressure, when both inlets are simultaneously supplied with a fluid pressure. In the case of identical pressures the switching position is indifferent and the outlet is connected only with one or simultaneously with both inlets. If at the inlet there is a pressure difference, then only the lower pressure will appear at the outlet. 
     The same product catalog mentions an OR gate valve on page 11.5/10-1, which also possesses two inlets and one outlet. In this case higher of the two inlet pressures always arrives at the outlet. The inlet supplied with the lower pressure is shut off. 
     The German patent publication DE 22 51 963 A discloses a logical valve gate with an inlet and two outlets. In this case the pressure medium flowing in through the permanently open inlet is alternatingly let off through the two outlets, a change over always taking place when the input pressure returns to zero or is reduced by a predetermined amount. 
     In safety related fluid power circuits, where safety plays a substantial role, there may be a requirement to supply a load simultaneously at all times from two pressure source and to shut off the supply for reasons of safety, when one of the two pressures falls below a certain threshold, for example because of a leak occurring. There is consequently a requirement for a fluid power circuit, which unlike the above mentioned known AND valve, separates a load completely from the pressure supply, when on the inlet side a certain pressure difference occurs. 
     SUMMARY OF THE INVENTION 
     Accordingly one aim of the present invention is to provide measures to separate an outlet completely from the fluid supply when there is an excessive pressure difference on the inlet side. 
     This object is to be attained in the case of a valve having the initially mentioned features because two second passages, connected with respectively one of the two inlets, are present which are respectively a component of one of two passage members adapted to move in relation to the valve housing in the actuating direction of the valve member, such passage members being so biased by stressing means independently of one another in a yielding manner into a home position that the valve member prior to reaching its terminal positions can bear, dependent on its actuation direction, on the one or other passage member and thereby can close its second passage so that the associated inlet is separated from the outlet, the level of the stressing force defining a threshold value for the inlet pressure difference, and on the threshold value being exceeded the valve member can force back the passage member, which is stressed and closed by it in order to shift into one of the terminal positions and accordingly to separate both inlets from the outlet. 
     The valve in accordance with the invention allows flow through of a pressure medium to the outlet when the same input pressure obtains at the two inlets. Should the flow through member at the inlet side exceed a threshold value defined by the stressing means, the outlet is separated from the two inlets. This takes place because the valve member on the one hand closes the first passage in the housing associated with the one inlet and on the other hand at the same time closes the second passage (associated with the other inlet) at one of the movable passage members. As long as there is a pressure difference on the inlet side not exceeding the predetermined limiting value, the valve member will separate, by cooperation with the corresponding passage member, only the inlet which is at the lower input pressure, with the result that the outlet will continue to be supplied from the other inlet with the higher input pressure. 
     The valve may for example be employed as a safety valve, it performing a logic function and produces a signal at the outlet only as long as a certain pressure difference is not exceeded. The valve may for example also be utilized to govern the synchronization of two control valves placed upstream from the two inlets. An output is then only produced when the two control valves produce pressure signals with the same level within a predetermined tolerance range. 
     Advantageous further developments of the invention are recited in the dependent claims. 
     It is preferred for the two first passages to be each provided with a first valve seat (having a first sealing face opposite it) arranged on the housing. In the two terminal positions the respectively one first passage is shut off, since the first sealing face opposite it engages its valve seat. The other first passage is in this case open, but despite this no fluid flows through it, because simultaneously the second passage, arranged on the associated passage member, is shut off. 
     Preferably one respective first sealing face and one second sealing face are disposed in pairs on two spaced apart closure member disk of the valve member. 
     The passages are more particularly so arranged that respectively one first passage in the housing and one second passage arranged in a passage member are placed in series for fluid-flow. 
     The home position of the passage members is preferably respectively defined by an abutment face disposed on the valve housing against which the associated passage member is thrust by the stressing means. 
     Preferably the valve member is placed in the actuating direction axially between the two passage members, i.e. it is preferably flanked on axially opposite sides by same. 
     The passage members are preferably circular in design with the formation of an associated second passage. They can be mounted in a sliding fashion like a piston on the valve housing. Preferably they are arranged coaxially in relation to the valve member. 
     Each passage member preferably bears a seal at which it is in constant sealing contact with the valve housing while allowing its sliding movement. In order to avoid having a dynamic seal it is possible in the alternative it is also possible to provide a respectively statically mounted membrane on the passage member and on the housing as a sealing element. 
     The stressing means are preferably in the form of a compression spring means, in particular of a mechanical kind. However it would also be possible to have gas spring and more particularly a pneumatic spring. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following the invention will be explained in detail with reference to the accompanying drawings. In longitudinal section they show a preferred embodiment of the valve having an AND gate function in various different positions of switching. 
         FIG. 1  shows the valve in a switching state simultaneously connecting both inlets with the outlet. 
         FIG. 2  shows the valve in s switching position, in which on the inlet side there is a pressure difference still below the threshold value and accordingly the outlet is connected with the inlet, which is at the higher pressure and is separated from the inlet at a lower pressure. 
         FIG. 3  shows a position of switching in which, owing to a pressure difference exceeding the threshold value, the valve member is shifted into one of its two possible terminal positions and accordingly the outlet is separated from the two inlets. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The valve generally referenced  1  is designed in the form of a spool valve and possesses an elongated slide-like valve member  2 , which is arranged in the interior of a valve housing  3  where it can perform a linear switching over movement  4  as indicated by a double arrow in the direction of its longitudinal axis  5 . 
     In the interior of the valve housing  3  an elongated recess  6  is formed, whose longitudinal axis  7  coincides with that ( 5 ) of the valve member  2 . The valve member  2  is received in the recess  6 . 
     The recess  6  has a middle portion  8  into which an outlet duct  12  of the valve housing  3  extending to an outlet A, which is accessible from the outside, opens. The middle portion  8  is adjoined axially on either side by a respective intermediate portion  13   a  and  13   b , which is larger in cross section, of the recess  6 , the transition between the middle portion  8  and each intermediate  13   a  and  13   b  being delimited by an axially orientated first passage  14   a  and  14   b . Each of these two first passages  14   a  and  14   b  is surrounded by a first valve seat  15   a  and  15   b  axially facing the adjoining intermediate portion  13   a  and  13   b , such seat being formed on the valve housing  3 . The two first valve seats  15   a  and  15   b  face in mutually opposite directions in the axial direction of the longitudinal axis  7 . 
     Each intermediate portion  13   a  and  13   b  is adjoined in the direction of the longitudinal axis  7  on the side opposite to the middle portion by a terminal portion  16   a  and  16   b  of the recess  6 . The terminal portion  16   a  and  16   b  has, at least in the region directly adjoining an intermediate portion  13   a  and  13   b , a larger cross section than the adjoining intermediate portion  13   a  and  13   b  so that an annular shoulder is formed, which defines an annular abutment face  17   a  and  17   b  facing the respective terminal portion  16   a  and  16   b.    
     The one, first terminal portion  16   a  is permanently joined by way of a first input duct  18   a  with a first inlet E 1  formed on the valve housing  3 . In a similar fashion the opposite second terminal portion  16   b  communicates via a second input duct  18   b  with a second inlet E 2 , independent from the first inlet E 1 , on the valve housing  3 . 
     In each of the second terminal portions  16   a  and  16   b  a passage member  23   a  (which is designed in a form separate both from the valve housing  3  and also from the valve member  2 ) having a second passage  22   a  and  22   b  extending through it axially, is arranged. Each passage member  23   a  and  23   b  is able to move in the direction of the switching over movement  4  in relation to the valve housing  3 . In the present example it is guided for axial motion on the internal peripheral face  24  of the associated terminal portion  16   a  and  16   b  like a piston element. By way of an annular seal  25  arranged at its outer periphery each passage member  23   a  and  23   b  is sealed off by a sealing effect between it and the valve housing  3  irrespectively of the currently assumed axial position. 
     The passage member  23   a  and  23   b  is so disposed inside the terminal portion  16   a  and  16   b  that it always assumes a position between the adjacent intermediate portion  13   a  and  13   b  and the opening region of the input duct  18   a  and  18   b  opening into the associated terminal portion  16   a  and  16   b . Accordingly each inlet E 1  and E 2  is joined, independently of the current position of sliding of the associated passage member  23   a  and  23   b , with the second passage  22   a  and  22   b  axially extending through the passage member  23   a  and  23   b.    
     The second passage  22   a  and  22   b  extends through the passage member  23   a  and  23   b  more especially centrally so that the latter is annular in form. It is arranged coaxially to the valve member  2 , the valve member  2  being placed axially between the two passage members  23   a  and  23   b.    
     Every second passage  22   a  and  22   b  is surrounded on the terminal side, facing the intermediate portion  13   a  and  13   b , by a second valve seat  26   a  and  26   b  formed on the passage member  23   a  and  23   b . The valve seat may therefore be shifted jointly with the associated passage member  23   a  and  23   b  in the direction of the switching over motion  4  in relation to the valve housing  3 . 
     The valve member  2  is provided, in the regions lying within the intermediate portions  13   a  and  13   b , with a respective closure disk  27   a  and  27   b . These closure disks  27   a  and  27   b  are for example a ring element consisting of sealing material, and more particularly of rubber-like elastic material, which is attached to an elongated principal member  28  consisting for example of metal or a hard synthetic resin material, of the valve member  2  with a radial overlap. Each closure disk  27   a  and  27   b  has, at its opposite terminal faces, two sealing faces, which face away from each other, that is to say on the one hand a first sealing face  32   a  and  32   b  facing the first valve seat  15   a  and  15   b  and on the other hand a second sealing face  33   a  and  33   b  facing the second valve seat  26   a  and  26   b . The two first sealing faces  32   a  and  32   b  are turned toward each other, whereas the second sealing faces  33   a  and  33   b  are turned away from each other in the direction of the switching over motion  4 . 
     In each terminal portion  16   a  and  16   b  of the recess  6  stressing means  34   a  and  34   b  are accommodated, which respectively take effect between the valve housing  3  and the associated passage member  23   a  and  23   b  and urge the latter into a home position indicated for example in  FIG. 1 , in which the passage member  23   a  and  23   b  engages the abutment face  17   a  and  17   b  assigned to it. The stressing means  34   a  and  34   b  accordingly urge the passage member  23   a  and  23   b  respectively toward the valve member  2  against the associated abutment face  17   a  and  17   b  on the housing. 
     The stressing means  34   a  and  34   b  on each side are designed separately from one another. They stress the associated passage member  23   a  and  23   b  in a yielding manner applying a respective force F B . Preferably the stressing means  34   a  and  34   b  are each 
     H constituted by a respective mechanical compression spring means, as for example in the form of a helical compression spring, extending between the associated passage member  23   a  and  23   b  and a terminating wall  35   a  and  35   b  of the valve housing  3 , said terminating wall  35   a  and  35   b  being axially opposite to the passage member  23   a  and  23   b  and hermetically sealing off the terminal portion  16   a  and  16   b  from the outside. 
     The level of the stressing force F B  is dependent on the configuration of the compression spring means. If required adjustment means may be present, with which the biasing effect of the stressing means  34   a  and  34   b  can be varied in order to predetermine the stressing force F B  as desired. 
     The stressing forces  34  F B  exerted on the two passage members  23   a  and  23   b  by the two stressing members  34   a  and  34   b  are preferably equal in size. 
     In lieu of a mechanical compression spring means it would for example be possible also be possible to have a pneumatic spring means and in particular one based of a trapped volume of air. 
     The valve member  2  extends through the middle portion  8  and extends into the adjoining intermediate portions  13   a  and  13   b  and, in a corresponding switching position, will also extend some distance into the adjoining terminal portion  16   a  and  16   b.    
     By way of the two inlets E 1  and E 2  a respective fluid medium may be supplied, the valve  1  preferably being operated with compressed air. Nevertheless other mediums may also be employed. 
     Via the respective input duct  18   a  and  18   b , the following terminal portion  16   a  and  16   b  and the following second passage  22   a  and  22   b  the valve member  2  is acted upon on opposite sides respectively by the pressure medium supplied via the two inlets E 1  and E 2 . The terminal working faces relevant here of the valve member  2  are equal in size and are indicated at  36   a  and  36   b . The pressure medium supplied via the inlet E 1  acts at a first input pressure P E1  in the one actuating direction on the valve member  2 , whereas the pressure medium supplied via the second inlet E 2  acts with a second input pressure P E2  in the opposite direction on the valve member  2 . 
     The output pressure P a  effective at the outlet A acts in both directions of actuations on the valve member  2 , the areas subjected to it also be equal so that to this extent there is a pressure compensation. 
     As a consequence the respective switching position of the valve member  2  and therefore of the valve  1  is set by the input pressure difference between the first and the second input pressure P E1  and P E2 . The valve member is acted upon in the direction of the lower input pressure by a dependent switching over force resulting from the input pressure difference. 
     The first and the second valve seats  15   a  and  15   b  and also  26   a  and  26   b  and in addition the first sealing faces  32   a  and  32   b  and the second sealing faces  33   a  and  33   b  are so matched in their design and arrangement that when one of the second sealing faces  33   a  or  33   b  engages the second valve seat  26   a  and  26   b  of a passage member  23   a  and  23   b  in its home position, all other sealing faces will be lifted clear of the respective valve seat associated with them. One of these two possible intermediate positions of the valve member  2  is indicated  FIG. 2 . 
     If a sufficiently high actuating force acts on the valve member  2 , the latter may be shifted past the said intermediate position ( FIG. 2 ) farther into a terminal position. This terminal position is defined by the first sealing face  32   a  or  32   b , facing in the switching over direction, engaging the oppositely placed first valve seat  15   a  and  15   b  with the result that the associated first passage  14   a  and  14   b  is shut off. These terminal positions are furthermore characterized in that the valve member  2  has then shifted the passage member  23   a  and  23   b , placed to the fore of it in the actuating direction, out of the home position against the actuating force F B  acting on it. The displacement is caused by the second sealing face  33   a  or  33   b , currently orientated in the actuating direction, such second sealing face  33   a  or  33   b  exerting a corresponding thrust force  37  on the opposite second valve seat  26   a  or  26   b  and consequently on the associated passage member  23   a  and  23   b . The second passage  22   a  or  22   b  of the passage member  23   a  or  23   b , thrust back by this, is then closed. The opposite force also responsible for the sealing action provides the stressing force F B  acting on the passage member  23   a  and  23   b.    
     One of the two possible terminal settings of the valve member  2  is illustrated in  FIG. 3 . 
     In a preferred application the valve is employed as a safety valve or as a logical valve, which at the outlet A only leads to the output of a pressure medium supplied at the inlet when the pressure difference between the input pressures P E1  and P E1  simultaneously present at the two inlet E 1  and E 2  does not exceed a predetermined threshold value. On the pressure difference threshold value being exceeded the valve separates the outlet A both from the first inlet E 1  and also from the second inlet E 2 . 
     The threshold value (responsible for the switching over characteristic of the valve) of the input side pressure difference is set by the stressing force F B  of the stressing means  34   a  and  34   b . The valve member  2  switches over into a terminal position separating the two inlets E 1  and E 2  from the outlet A, when the resulting actuating force acting on the valve member  2  on the basis of the input side pressure difference is larger than the stressing force F B , acting in the opposite direction, of the one or the other stressing means  34   a  and  34   b.    
       FIG. 1  shows an operating state with identical input pressures P E1  and P E2 . The valve member  2  assumes in this case an indifferent switching position, which can vary, there being either a flow (indicated by the added flow arrows) simultaneously from both inlets E 1  and E 2  of the pressure medium to the outlet A or merely from one of the two inlets E 1  or E 2 . 
     The outlet A is furthermore supplied with the higher of the two input pressures P E1  and P E2 , when there is a pressure difference at the input, which has still not exceeded the set threshold value. Such an intermediate position is depicted in  FIG. 2 . Owing to the first input pressure P E1 , which is somewhat higher than the second input pressure P E2 , the valve member  2  will have turned off the second passage  22   b  of the passage member  23   b  (associated with the second inlet E 2 ), and the first and second passages  14   a  and  22   a  (connected for fluid flow in series) simultaneously associated with the first inlet E 1  are open in order to allow the passage of the first higher input pressure P E1  to the outlet A. 
     In this intermediate position the valve member  2  bears against the passage member  23   b  (associated with the second inlet E 2 ) which is fixed in its home position by the associated stressing means  34   b.    
     If the input pressure difference exceeds the predetermined threshold value, the valve member  2  in accordance with  FIG. 3  can force back the passage member  23   b  assigned to the lower input pressure P E2  overcoming the stressing force F B  stressing it. This displacement movement ends, when the valve member  2  abuts the first valve seat  15   a . This means that both the first passage  14   a  is shut off and also the second passage  22   b  formed on the shifted passage member  23   b  is also shut off. Therefore the connection between the outlet A and each of the two inlets E 1  and E 2  is interrupted. 
     The manner of operation described is possible in either direction of movement of the valve member  2  and is only dependent on which of the two input pressures E 1  and E 2  is higher than the other one. 
     The valve  1  ensures that the outlet A is completely shut off from the inlets E 1  and E 2  on reaching an input side pressure difference of a predetermined size but that the outlet A is supplied with the higher of the two currently available input pressures until the threshold value is reached.