Abstract:
A magnetic drive for a valve, in particular for a pneumatic or hydraulic valve, includes a movable armature ( 14 ) and a permanent magnet ( 20 ). The permanent magnet ( 20 ) is formed from a magnetic paste or a magnetic foil. In preferred embodiments, the permanent magnet ( 20 ) is integrated into the movable armature ( 14 ) and cooperates with a fixed solenoid.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a magnetic drive for a valve, in particular for a pneumatic or hydraulic valve. 
     From German patent application DE 102 07 828 A1 a magnetic drive comprising a polarized movable armature is known. The armature includes a permanent magnet in the form of a ring magnet, which is arranged between two rings conducting the magnetic flux. The ring magnet is polarized perpendicularly to the direction of movement of the armature. 
     In German patent specification DE 197 22 013 C2 a magneto-mechanical power system is shown in which a pole plate resting on an solenoid is raised when the solenoid is energized. Here, the magnetic flux is partially displaced into a shunt air gap which is formed between a neck of a flux conductor plate and the wall of a soft-iron pot of the solenoid. 
     It is an object of the invention to provide a compact magnetic drive for a valve showing a minimized switching or continuous duty. 
     BRIEF SUMMARY OF THE INVENTION 
     The magnetic drive according to the invention comprises a movable armature and a permanent magnet. The permanent magnet is formed from a magnetic paste or from a magnetic foil. The invention is based on the finding that magnetic paste or foil blanks are fabricable, from which specificially shaped permanent magnets are able to be realized. Even complicated shapes are possible, if required. Therefore, the permanent magnet can be “custom-made” for the respective requirements, in particular with regard to its three-dimensional shape. 
     The permanent magnet formed from the magnetic paste or foil can generally represent a portion of the magnetic drive. In the preferred embodiments of the invention, the magnetic drive comprises a fixed solenoid the permanent magnet being integrated into the movable armature and co-operating with the fixed solenoid. 
     According to a preferred design, the armature comprises at least a first part and a second part. The armature is movable in an axial direction. The permanent magnet is arranged between the first part and the second part with respect to the axial direction. 
     The first and second parts are preferably constructed in a plate shape. The second part lies directly opposite the solenoid. The first part has an extension extending in axial direction towards the solenoid. 
     In addition, in the preferred embodiment, a radial secondary gap is formed between the extension of the first part and the second part with respect to the axial direction. 
     A magnetically non-conducting material may be arranged in the secondary gap. 
     With a suitable selection of the material and the geometry of the components of the solenoid and of the armature, also with respect to the surrounding parts (e.g. in view of a translatory or rotary drive movement of the armature), a plurality of valve functions can be realized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the basic structure of a magnetic drive according to the invention, in sectional view; 
         FIG. 2  shows the magnetic flux lines in a magnetic drive according to the invention, with the armature in a non-resting position and the solenoid applied with positive current; 
         FIG. 3  shows the magnetic flux lines with the armature in a resting position and a currentless solenoid; 
         FIG. 4  shows the magnetic flux lines with the armature being in a resting position and the solenoid applied with negative current; 
         FIGS. 5   a  and  5   d  show diagrammatically illustrated variants of the magnetic drive according to the invention; and 
         FIG. 6  shows a valve with a magnetic drive according to the invention, in sectional view. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The basic structure of a magnetic drive for a valve according to the invention can be seen from  FIG. 1 . A pot  10  with a coil  12  wound concentrically around a central axis A of the pot  10  forms an solenoid in a known manner. The pot  10  has an E-shaped cross-section with a central part  10   a  and a wall  10   b.  An armature  14 , movable in the direction of the axis A, is arranged opposite the solenoid. The armature  14  comprises a first part  16  and a second part  18  lying directly opposite the solenoid. The first and second parts  16 ,  18  both are substantially plate-shaped and extend perpendicularly to the axis A. 
     A permanent magnet  20  is arranged between the two parts  16  and  18 . The first part  16  has on its edge side an extension  22 , directed towards the solenoid, which lies opposite the solenoid. The gap between the second component  18 , in particular the extension  22 , and the solenoid is referred to as working air gap  24 . A radial gap which is referred to as secondary gap  26  is provided between the extension  22  and the second part  18 . A magnetically non-conducting material, e.g. a plastic ring (not shown), may be arranged in the secondary gap  26 . The armature  14  may be coupled to a spring element (not shown in  FIG. 1 ) which exerts onto the armature  14  a pre-stressing force directed away from the solenoid. 
     The permanent magnet  20  is formed from a magnetic paste on the basis of a NdFeB powder, with which very specific magnet shapes can be realized. Alternatively, the permanent magnet  20  may also be formed from magnetic foils which are specifically cut to size (foil-cast layers) which are likewise produced on the basis of a NdFeB powder. The permanent magnet  20  is polarized in axial direction. 
       FIG. 2  shows the course of the magnetic flux lines in a magnetic drive according to the invention, with the armature  14  in a non-resting position and the solenoid applied with positive current. In this case the magnetic field of the solenoid induced by the coil  12  is added to the magnetic field of the permanent magnet  20 . Therefore, on the one hand, a flux is produced from the central part  10   a  of the pot  10  via the working air gap  24  through the second part  18  into the permanent magnet  20 , and, on the other hand, from the permanent magnet  20  through the second part  18  via the secondary gap  26  into the extension  22  of the first part  16  and again via the working air gap  24  into the wall  10   b  of the pot  10 . The first part  16  provides for a “short circuit” of the lines of flux entering in axial direction into the permanent magnet  20  and emerging from the permanent magnet  20 . This path of flux results in an attractive force of the solenoid onto the armature  14 . This force is possibly greater than the pre-stressing force of the spring element, so that the armature  14  moves towards the solenoid (stroke), until it rests on the solenoid. 
     This state is illustrated in  FIG. 3  with the solenoid being currentless. The working air gap  24  is closed, so that the magnetic flux lines pass directly from the central part  10   a  of the pot  10  into the second part  18  and from the extension  22  of the first part  16  into the wall  10   b  of the pot  10 . 
     In order to move the armature  14  away from the solenoid again (restoring), the solenoid is applied with negative current, i.e. the magnetic field induced by the coil  12  is directed against the field of the permanent magnet, so that a repelling force is exerted onto the armature  14 . The corresponding course of the magnetic flux lines is shown in  FIG. 4 . The secondary gap  26  again makes the passage of the flux lines possible from the second part  18  to the extension  22  of the first part  16 , in this case for the formation of a closed magnetic circuit of the permanent magnet  20 . 
     A material arranged in the secondary gap  26  ensures that the dimensions of the secondary gap  26  remain constant. 
     In  FIGS. 5   a  to  5   d,  four different variants of a magnetic drive according to the invention are illustrated diagrammatically, which are characterized with the aid of the following Table: 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                 bistable/ 
                   
               
               
                   
                 Spring element 
                 monostable 
                 switching current 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Variant 1 (FIG. 5a) 
                 + 
                 b 
                 i+; i− 
               
               
                 Variant 2 (FIG. 5b) 
                 − 
                 b 
                 i+; i− 
               
               
                 Variant 3 (FIG. 5c) 
                 + 
                 m 
                 i+; i + H 
               
               
                 Variant 4 (FIG. 5d) 
                 − 
                 m 
                 i+ 
               
               
                   
               
             
          
         
       
     
       FIG. 6  shows an application of the magnetic drive according to the invention in a fluid valve. A valve body  30 , which is pre-stressed by means of a spring element  28  (here: a form spring), closes a valve seat  32 , formed between a pressure connection P and a working connection A, with a seal  34 . The valve body  30  is coupled to the armature  14  of the magnetic drive, which raises the armature  14  when the solenoid is applied with positive current, so that the valve seat  32  is freed. The restoring takes place either solely through the force of the spring element  28  or assisted by the solenoid being applied with a negative current.