Abstract:
With a magnet arrangement for an electromechanical drive with a cylindrical armature guided in a pole tube, the position of the armature is transformed into an electrical signal. Provided for this is a displacement sensor which is connected to the armature and has a fixed part and a movable part. One side of the armature is formed such that it transfers the movement of the armature, and the other side of the armature is connected to the movable part of the displacement sensor. The pole tube is provided with a closure part on the side of the displacement sensor. A pressure tube is led to the outside through an axial clearance of the closure part. The movable part of the displacement sensor moves in the pressure tube. The pressure tube is enclosed by the fixed part of the displacement sensor. In order to prevent the displacement sensor from being damaged by vibrations, the fixed part of the displacement sensor is arranged in a clearance of the closure part. Such type magnet arrangements of this type are preferably used for electrical position feedback in fluidic valves.

Description:
FIELD AND BACKGROUND OF THE INVENTION 
     The invention relates to a magnet arrangement for an electromechanical drive, especially for a fluidic valve with a cylindrical armature guided in a pole tube and with a magnetic coil enclosing the pole tube and with a displacement sensor which transforms the position of the armature into an electrical signal and has a fixed part and a movable part, in which arrangement one side of the armature is formed for transferring the movement of the armature and the other side of the armature is connected to the movable part of the displacement sensor, the pole tube being provided with a closure part on the side of the displacement sensor. 
     SUMMARY OF THE INVENTION 
     A magnet arrangement of this type is known as a component part of a hydraulic directional control valve from the publication “Neuartige, kostengünstige Antriebe für Proportionalventile in der Fluidtechnik” [novel, low-cost drives for proportional valves in fluid technology], the journal “O+P Ölhydraulik und Pneumatik” [O+P oil hydraulics and pneumatics] 43 (1999) No. 4, pages 252 to 258. Arranged in an axially displaceable manner in the housing of a directional control valve is a control piston, which controls the magnitude of the stream of pressure medium flowing via the directional control valve. In axial extension of the control piston, a pole tube is respectively screwed into the housing from each of both sides. Pushed over each pole tube is a coil. Guided in each of the two pole tubes is a cylindrical armature, which exerts a force deflecting the control piston when current is applied to the coil enclosing it. Connected to one of the armatures is a displacement sensor, which transforms the position of the armature into an electrical output signal, which is a measure of the position of the armature. Since the control piston of the directional control valve is non-positively coupled to the armature, the electrical output signal of the displacement sensor is also a measure of the position of the control piston. The displacement sensor has a fixed part in the form of a coil arrangement and a movable part, the core. The core is held on a core support, which is held on the armature on the side remote from the control piston. The pole tube is closed off on the side of the displacement sensor by a closure part, which is provided with an axial clearance. Through this clearance, a pressure tube is led out of the pole tube to the outside. The closure part and the pressure tube led through the latter close off the armature space from the outside in a pressure-tight manner. The part of the pressure tube protruding beyond the closure part in the axial direction is concentrically enclosed by a coil arrangement, which forms the fixed part of the displacement sensor. The coil arrangement is arranged in a housing of its own. This housing is held on the pole tube by a clamping clip, which engages in an outer annular groove of the closure part. Additionally provided is a serration, which prevents the housing from turning with respect to the pole tube. The core of the displacement sensor moves in the region of the pressure tube enclosed by the coil arrangement. The housing of the fixed part of the displacement sensor bears against the coil and secures the coil in the axial direction. This type of fixing of the coil is more complex than the fixing of the coil by a nut which engages in an external thread on the closure part, as is customary in the case of a pole tube without a displacement sensor, and increases the number of different parts. The arrangement of the displacement sensor in axial extension of the pole tube makes the directional control valve provided with the displacement sensor susceptible to vibrations, which in an extreme case may lead to the displacement sensor being torn off. 
     The invention is based on the object of providing a magnet arrangement of the type stated at the beginning in which the risk of damage caused by vibrations is significantly reduced. 
     According to the invention the fixed part ( 28   a  to  28   c ,  36 ;  28   a  to  28   c    69 ) of the displacement sensor is arranged in a clearance ( 24 ) of the closure Part  13 ;  50 ;  67 ;  87 ;  100 ). Since the entire displacement sensor is arranged inside the closure part of the pole tube, a very compact construction of the magnet arrangement, in which the displacement sensor is also protected from mechanical damage, is obtained. A separate housing is not required for the fixed part of the displacement sensor. Moreover, there is no longer any need for measures for fastening such a housing on the pole tube. The closure parts containing the fixed part of the displacement sensor can be produced and tested on their own. 
     Advantageous developments of the invention are also presented. They comprise structural design details of the magnet arrangement, in particular those which allow a simple arrangement of the electronic components of a circuit arrangement for evaluating the output signals of the displacement sensor and also a simple connection of external electrical lines. Structural design measures which concern the configuration of the closure part of the pole tube are also presented. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained below more precisely with its further details on the basis of exemplary embodiments represented in the drawings, in which: 
         FIG. 1  shows a section through a magnet arrangement formed according to the invention, 
         FIG. 2  shows the region of the closure part of the magnet arrangement represented in  FIG. 1  in an enlarged representation, 
         FIG. 3  shows a section through a further closure part with a terminating part for a magnet arrangement according to the invention, 
         FIG. 4  shows a section through a third closure part with a terminating part for a magnet arrangement according to the invention, 
         FIG. 5  shows a section through the terminating part represented in  FIG. 4 , 
         FIG. 6  shows a section through a fourth closure part for a magnet arrangement according to the invention and 
         FIG. 7  shows a section through a further closure part with a terminating part, the closure part and the terminating part being connected to each other by means of a screw drive. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The same components are provided in the figures with the same designations. 
       FIG. 1  shows a section through a magnet arrangement  10  with a pole tube  11 , an armature  12  guided in the pole tube  11  and a closure part  13 . The pole tube  11  is screwed into a housing  14  of a fluidic valve, only represented schematically. Formed onto the armature  12  on the side facing the housing  14  is a tappet  15 , which deflects a control piston (not represented here) of the valve. An only schematically represented magnetic coil  16  encloses the pole tube  11 . The magnetic coil  16  is held between the housing  14  and a nut  17 , which engages in an external thread  18  of the closure part  13 . Arranged between the armature  12  and the closure part  13  is a spring  19 . The spring  19  ensures a defined position of the armature  12  when the magnetic coil  16  is not energized. The spring  19  is no longer needed if a defined position of the armature  12  with the magnetic coil  16  deenergized is ensured in some other way. If the magnetic coil  16  is energized, the armature  12  is correspondingly deflected. Arranged on the side of the armature  12  facing the closure part  13  is a core holder  21 , provided with a core  20 . The core  20  forms the movable part of a displacement sensor. The displacement sensor transforms the position of the armature  12  into an electrical signal, which is a measure of the position of the armature  12 . The closure part  13  is provided with a clearance  24 , which is sealed by a terminating part  25 . Details of the connection of the terminating part  25  to the closure part  13  are not specifically represented. The two parts may, for example, be adhesively bonded to each other. Integrated into the end face of the terminating part  25  is a connector  26 . The terminating part  25  is provided with a clearance  27 , which goes over into the clearance  24  of the closure part  13 . A coil arrangement, comprising two secondary coils  28   a  and  28   b  and also a primary coil  28   c  surrounding the latter, forms together with a support  36  the fixed part of the displacement sensor. The support  36  with the coils  28   a ,  28   b  and  28   c  is arranged in the clearance  24  of the closure part  13 . The coils  28   a  and  28   b  as well as  28   c  are arranged concentrically in relation to the core  20 . Further details of the displacement sensor are described on the basis of  FIG. 2 . 
       FIG. 2  shows a detail from the magnet arrangement  10  represented in  FIG. 1 , in an enlarged representation. Components which have already been described above are not described again in connection with  FIG. 2 . A pressure tube  29 , which is closed at one end and is provided at its open end with a collar  30 , protrudes into the clearance  24  of the closure part  13 . The collar  30  is supported on an annular face  21 , facing the armature  12 , of the closure part  13 . A peripheral weld  32  ensures a pressure-tight connection between the collar  30  of the pressure tube  29  and the closure part  13 . It is possible to dispense with the weld  32  if a pressure-tight connection between the collar  30  and the closure part  13  is established in some other way. As an alternative to this, it is possible to form the closure part and the pressure tube as one piece. The free end of the pole tube  11  is flanged into a first annular groove  33  of the closure part  13 . A sealing ring  34  is arranged between the closure part  13  and the pole tube  11  in a further annular groove  25 . In order that the magnetic coil  16  can be pushed onto the pole tube  11 , the outside diameter d 18  of the external thread  18  is chosen to be slightly smaller than the outside diameter d 11  of the pole tube  11 . Of the winding ends of the coils  28   a ,  28   b  and  28   c  arranged on the support  36 , two winding ends are represented, designated by  37  and  38 . In the simplest case, the winding ends  37  and  38  are connected directly to terminal pins  41 ,  42  of the connector  26 . It is also possible, as schematically represented in  FIG. 2 , for a printed circuit board  39 , which is loaded with electrical components  44 ,  45  of an electrical evaluation circuit, to be held on the terminal pins  41 ,  42  of the connector  26 . In this case, the winding ends  37 ,  38  are connected to the input of the evaluation circuit and the output of the evaluation circuit is connected to the terminal pins  41 ,  42 . 
       FIG. 3  shows a further closure part  50  with a terminating part  51 . As represented in FIGS.  1  and  2 —the printed circuit board  39  is held on the support  36  for the coils  28   a ,  28   b  and  28   c  of the fixed part of the displacement sensor. The support  36  has been pushed over a pressure tube  53 , which for its part is held on the closure part  50 . The pressure tube  53  is provided with a collar  54 . The collar  54  is supported on the annular face  31  of the closure part  50 . The collar  54  is provided on the side facing the armature  12  with a clearance  55 , which is formed as a guide for the spring  19  represented in  FIG. 1 . The collar  54  is connected in a pressure-tight manner to the closure part  50  by a peripheral weld  32 . The printed circuit board  39  is provided with soldering points  57  and  58 , to which the winding ends  37  and  38  are connected. An electrical cable  60  is led through the terminating part  51  in the axial direction. In the region where it passes through, the cable  60  is surrounded by a grommet  61 . Formed onto the terminating part  51  as an additional means for preventing kinking is a tubular continuation  62 , extending the terminating part  51 . The individual lines  63 ,  64  of the cable  60  are connected to further soldering points  65 ,  66  of the printed circuit board  39 . In the simplest case, i.e. when no evaluation circuit is provided, the soldering points  57 ,  58  are connected to the soldering points  65 ,  66 . In the exemplary embodiment represented in  FIG. 3 , the printed circuit board  39  is connected to an evaluation circuit schematically represented by the electronic components  44 ,  45 , the input of which is connected to the soldering points  57 ,  58  and the output of which is connected to the soldering points  65 ,  66 . 
       FIG. 4  shows a third closure part  67 , in which a terminating part formed as a plate  68  is screwed to the closure part  67 . Formed onto the plate  68  is the connector  26  with the terminal pins  41 ,  42 . The printed circuit board  39  is mechanically held on the terminal pins  41 ,  42 . As represented in  FIG. 2 , the support  36  is held on the printed circuit board  39 . The unit formed by the plate  68 , the terminal pins  41 ,  42 , the printed circuit board  39  and the support  36  has been pushed over the pressure tube  53 . The printed circuit board  39  with the schematically represented electrical components  44 ,  45  of an evaluation circuit is arranged in a clearance  70  of the plate  68 . The winding ends  37 ,  38  of the coils  28   a ,  28   b ,  28   c  are connected to the input of the evaluation circuit. The terminal pins  41 ,  42  of the connector  26  are electrically connected to the output of the evaluation circuit. The plate  68  is held on the closure part  67  by screws distributed over the circumference, two of which screws  77 ,  78  can be seen in  FIG. 4 . 
       FIG. 5  shows a section along the line B—B represented in  FIG. 4 . In this representation, two further screws  79  and  80  in addition to the screws  77  and  78  can be seen. In this section, two further terminal pins  81 ,  82  and also two further electronic components  84 ,  85  can also be seen. 
       FIG. 6  shows a further closure part  87 . The production of the terminating part of the closure part  87  takes place—as described below—by encapsulating with plastic. The pressure tube  53  protrudes into the clearance  24  of the closure part  87  and is connected to it in a pressure-tight manner. The support  36  with the coils  28   a ,  28   b ,  28   c  has been pushed over the pressure tube  53 . The printed circuit board  39  is held on the support  36 . The terminal pins  41 ,  42  are mechanically held on the printed circuit board  39 . This formation is inserted into an only schematically represented multi-part mold, which comprises a base plate  90 , two mold halves  91   a ,  91   b  and an insert  92 . Together with the insert  92 , the mold halves  91   a ,  91   b  enclose a space  24 , which determines the later shape of the terminating part and of the connector formed onto the latter. The mold halves  91   a ,  91   b  are divided along a plane running through the center axis of the closure part  87 , in such a way that demolding of the closure part provided with the terminating part and the connector is possible. During encapsulation, the space  94  and the clearance  24  are filled with liquid plastic via an only schematically represented channel  95 . In order that the plastics compound can distribute itself uniformly in the mold, vent holes are provided in the customary way in the mold and/or in the closure part  87 . They are not represented in  FIG. 6 . Since the plastic also touches parts of the electrical circuit, it is necessary to use an electrically insulating plastic for the terminating part. For demolding the closure part  87  provided with the terminating part and connector, after the plastics compound has solidified the mold halves  91   a  and  91   b  are pulled apart laterally and the insert  92  is pulled out upward. 
       FIG. 7  shows a closure part  100 , to which a terminating part  101  is connected by means of a screwed connection. Wherever details which have already been described in connection with previous figures are represented in  FIG. 7 , the same designations as in the previous figures are used hereafter for the corresponding components. The pressure tube  29  protrudes into the cylindrically formed clearance  24  of the closure part  100 . It is supported with its collar  30  on the end face, facing the armature of the magnet arrangement, of the closure part  100 . The clearance  24  of the closure part  100  is provided with an internal thread  104 , and the terminating part  101  is provided with a corresponding external thread  105 . The internal thread  104  of the closure part  100  and the external thread  105  of the terminating part  101  form a screw drive, which transforms a rotational movement of the terminating part  101  with respect to the closure part  100  into an axial movement between the two parts. The printed circuit board  39  is held on the terminating part  101 . Held on the printed circuit board  39  are the support  36  with the coils  28   a ,  28   b  and  28   c , which form the fixed part of the displacement sensor. The region of the terminating part  101  in which the support  36  with the coils  28   a  to  28   c  is located is arranged inside the clearance  24  of the closure part  100 . The support  36  concentrically encloses the pressure tube  29 . The distance between the pressure tube  29  and the support  36  is chosen such that the support  36  can move with slight play with respect to the pressure tube  29 . Screwed onto the external thread  105  of the terminating part  101  is a check nut  108 , which is provided with an internal thread  107  and prevents unintentional turning of the terminating part  101  with respect to the closure part  100  during the operation of the displacement sensor. In order to secure the relative position of the terminating part  101  with respect to the closure part  100 , the check nut  108  is screwed against the closure part  100 , its internal thread  107  being supported on the external thread  105  of the terminating part  101 , and the end face provided with the designation  110  being supported on the closure part  100 . Formed onto the end remote from the closure part  100  of the terminating part  101  is the connector  26  with the terminal pins  41 ,  42 . The position of the core  20 , which forms the movable part of the displacement sensor, is represented by dashed lines. The axial distance between the fixed part and the movable part of the displacement sensor can be changed by turning the terminating part  101  with respect to the closure part  100 . The terms “fixed part” and “movable part” of the displacement sensor relate to the operation of the displacement sensor in which the armature of the magnet arrangement moves the core  20  and the support  36  with the coils  28   a  to  28   c  is arranged fixedly with respect to the valve housing. In order to adjust the displacement sensor, the core is held in a fixed position in relation to the valve housing and the terminating part  101  is turned with respect to the closure part  100 , and consequently with respect to the valve housing, until the electrical output signal present at the terminal pins  41 ,  42  has assumed a desired value. This position is secured, as described above, by tightening the check nut  108  against unintentional turning. 
     The configuration of the closure part and terminating part described on the basis of  FIG. 7  allows a zero displacement of the electrical output signal to be performed as and when required by mechanical means. With such a zero displacement it is possible, for example, to correct production-related tolerances with regard to the axial position of the fixed part of the displacement sensor. In addition, it is also possible, by an axial adjustment of the fixed part of the displacement sensor with respect to the closure part, to change the range of the electrical output signal, so that, for example, instead of an output signal which moves between a negative maximum value and a positive maximum value, an electrical output signal which moves between zero and a positive maximum value or between zero and a negative maximum value is obtained. 
     By combining the electrical output signal of the displacement sensor with predeterminable threshold values in the form of electrical signals, the steady output signal of the displacement sensor can be used as and when required to generate switching signals which signal the reaching of positions of the control piston of a directional control valve determined by the threshold values. The combining of the electrical signals may take place both outside the closure part and inside the closure part, for example by the arrangement of additional electronic components on the printed circuit board  39 . The switching signals are available in addition to the steady output signal of the displacement sensor and can be further processed independently of one another in devices for control and/or monitoring.