Abstract:
A shielded solenoid for a solenoid operated valve having a solenoid body and an annular coil of electrical wire in the solenoid body. An armature of magnetic material is rectilinearly movable with respect to the body. A magnet holder is fastened to the armature and has a permanent magnet fixedly oriented thereon. A shield member covers the magnet holder and the permanent magnet. The shield member is configured to shield a Hall effect sensor from any significant electromagnetic field produced by the coil when effecting rectilinear movement of the armature. The hollow shield member has a non-metallic plug closing one end thereof. The plug has the Hall effect sensor oriented therein to closely oppose the magnet on the magnet holder so that movement of the armature and resulting corresponding movement of the magnet will cause the Hall effect sensor to produce a signal indicative of movement of the armature.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a flow rate control valve, and more particularly, to a proportional solenoid operated valve having a shielded armature motion sensing feature. 
   BACKGROUND OF THE INVENTION 
   Solenoid valves have been conventionally used to control the flow rate of a fluid by using a solenoid to control valve activation. A conventional solenoid valve has a magnetic sensor, which is typically a Hall effect sensor, that effectively senses movement of a component and thus provides positional information for a moving component positioned in high pressure fluid in a fluid delivery device. 
   The Hall effect sensor used in motion sensing can offer enhanced reliability in extreme environments. A coil contained in the solenoid valve produces an electromagnetic field that may interfere with the accurate performances of the Hall effect sensor, but the prior art, such as Fukano et al., U.S. Pat. No. 6,666,429, does not have any protective mechanism to prevent external electromagnetic fields from interfering with the Hall effect sensor. 
   It is an object of the invention to provide a shield made of an appropriate protective material so that the performance characteristics of the Hall effect sensor are not compromised by external electromagnetic fields created by the solenoid coil. 
   SUMMARY OF THE INVENTION 
   The invention is directed to a shielded solenoid for a solenoid operated valve having a solenoid body and an annular coil of electrical wire in the solenoid body which has a central hole therethrough. A first hollow magnetic pole piece is oriented in the central hole adjacent a first axial end face of the annular coil. A second hollow magnetic pole piece is coaxially oriented with respect to the first pole piece in the central hole adjacent a second axial end face of the annular coil remote from the first axial end face and being magnetically isolated from and immovably fixed with respect to the first pole piece. An end of the second hollow pole piece has a non-magnetic plug member closing an open end thereat. An armature of magnetic material is rectilinearly movably displaceably mounted in the first and second hollow magnetic pole pieces. A non-magnetic rod part projects coaxially from at least one axially facing end thereof and is rectilinearly movable with the armature. The non-magnetic rod part has a magnet holder fastened thereto and has a permanent magnet fixedly oriented thereon. A hollow metallic shield member covers a segment of an outer periphery of the second pole piece whereat the magnet holder and the permanent magnet are oriented. The shield member is configured to shield a Hall effect sensor from any significant electromagnetic field produced by the coil when effecting rectilinear movement of the armature. The hollow shield member has a non-metallic plug closing one end thereof. The plug has the Hall effect sensor oriented therein to closely oppose the magnet on the magnet holder so that movement of the armature and resulting corresponding movement of the magnet will cause the Hall effect sensor to produce a signal indicative of movement of the armature. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and purposes of this invention will be apparent to persons acquainted with apparatus of this general type upon reading the following specification and inspecting the accompanying drawing, in which: 
       FIG. 1  illustrates a central, longitudinal cross sectional view of the proportional solenoid valve with a motion sensor in accordance with an embodiment of the invention; and 
       FIG. 2  is a fragmentary view of a modified shield member. 
   

   DETAILED DESCRIPTION 
   The solenoid portion  10  of a solenoid operated valve is illustrated in the drawing. The solenoid portion  10  includes a solenoid body  11  having a hollow cylindrical, non-metallic bobbin  12  on which is wound many turns of wire  13  to form an annular coil  14 . 
   The annular coil  14  is encased in a non-metallic synthetic resin shell  15  which has a radially outwardly extending flange  16  having a plug socket  17  formed therein so that electrical contact prongs  17 A are exposed in the socket for electrical connection to a plug not shown. The contact prongs  17 A are electrically connected to the wire  13  forming the annular coil  14  so as to facilitate the provision of electrical energy to the coil  14 . 
   In this particular embodiment, the shell  15  is oriented inside a steel cup  18  having a through-hole  20  in the bottom wall  19  thereof and with the flange  16  projecting through a slot  18 A in the rim of the open end of the cup  18 . The shell  15  is retained inside the steel cup  18  by press fitting a washer  18 B into the open end of the steel cup. In this particular embodiment, a compressible spring o-ring type seal  18 C is oriented between the washer  18 B and the shell  15 . 
   A first elongate hollow tubular magnetic pole piece  21  has an externally thread end section  21 A configured to screw into an internally threaded hole in a valve body not shown. The other end of the pole piece  21  is fixedly oriented inside the interior of the hollow bobbin  12 . 
   In this particular embodiment, the first pole piece  21  extends into the interior of the bobbin  12  a finite distance. A second elongate hollow tubular magnetic pole piece  22  is coaxially oriented with respect to and secured by an also coaxially oriented non-magnetic member  24 , and oriented about the mid-portion of the hollow interior of the bobbin  12 , to an end of the first pole piece  21  that is remote from the valve body. The second pole piece  22  extends a finite distance beyond the end of the bobbin  12  that is remote from the valve body and through and beyond the hole  20  in the bottom wall  19  of the steel cup  18 . It is beneficial for the clearance dimension between the inner diameter surface of the hole  20  and an outer diameter surface  23  of the pole piece  22  to be as small as is reasonable for assembly in order to optimize the magnetic shielding. 
   A non-magnetic, here brass, hollow plug  25  is secured to the open end of the second pole piece  22  by any convenient structure. Here, the plug  25  has a reduced diameter portion  26  receives therein the crimped open end  27  of the second pole piece  22 . In addition, the portion of the plug  25  extending axially beyond the pole piece  22  has an external thread  28  thereon, the purpose of which will be explained in more detail below. The axially facing end wall  25 A of the hollow plug  25  has a shallow centrally oriented recess  25 B therein, the purpose of which will be explained in more detail below. 
   A hollow armature  29  made of magnetic material is rectilinearly movably and displaceably mounted internally of the pole pieces  21  and  22 . A non-magnetic rod  31  extends through the interior of the armature  29  and is secured as by being pressed fit therein. Other forms of securement of the rod  31  to the armature  29  are to be considered as being within the scope of this invention. 
   In this particular embodiment, the rod  31  extends axially beyond both ends of the armature  29 . The end  32  of the rod  31  extends through the interior of the pole piece  21  and is operatively connected to a movable valve member (not illustrated) inside the valve body for controlling the flow of fluid through the valve body in a well understood way. The opposite end  33  of the rod  31  has a magnet holder  34  fixedly secured thereto and movable therewith. 
   In this particular embodiment, the magnet holder  34  has an opening in one end  35  into which the distal end  33  of the rod  31  is pressed fit. The opposite end  36  of the magnet holder  34  has an axially opening cup shaped opening  37  therein into which is fixedly oriented a permanent magnet  39 . In this particular embodiment, the outer diameter of the magnet holder  34  is conformed to the hollow interior of the plug  25  so as to be relatively movably and slidably received therein. 
   The hollow interior  30  of the armature  29  at an end from which the end  33  of the rod  31  extends is enlarged and is configured to attach to the magnet holder  34 . The attachment of the magnet holder  34  to the armature  29  can be formed by being pressed fit or by using a threaded connection. The magnet holder  34  also has a radially outwardly extending flange  38  thereon that is configured to abut against the end of the plug  25  oriented inside the pole piece  22 . 
   A hollow steel cylindrical shield member  40  having an internal thread  41  thereon oriented mid-length of the shield member  40  is threadedly secured to the external thread  28  on the plug  25 . The interior surface  40 A of the shield member  40  on one side of the internal thread  41  has a diameter closely conforming to the external diameter surface  23  of the second pole piece  22  so as to facilitate the interior part  42  of the shield member  40  snuggly sliding over the exterior surface  23  of the second pole piece  22 . A reduction of the clearance dimension between the outer diameter surface  23  and the inner diameter surface  40 A to as small as is reasonable for assembly is important for the purpose of optimizing the magnet shielding. 
   A synthetic resin plug  43  having a Hall effect sensor  47  encased therein is slidably received into an open end of the shield member  40  on a side of the internal thread  41  remote from the interior part  42 . 
   In this particular embodiment, the Hall effect sensor  47  is oriented at one end of the plug  43  close to an axially facing flat surface  44  of the plug  43  that opposes the shallow recess  25 B in the end wall  25 A of the plug  25 . The circumferential periphery of the plug  43  adjacent an end remote from the Hall effect sensor  47  has a reduced diameter section  45  forming a shoulder  46  onto which is provided a compressible spring  48 . 
   A cup shaped cap  49  having a central through-hole  50  in the bottom wall  51  through which extends the reduced diameter section  45  of the plug  43  is secured to the end of the steel shield member  40 . The segment of the bottom wall  51  surrounding the through-hole  50  serves as an abutment for the end of the compressible spring  48  that is oriented remote from the end abutting the shoulder  46 . 
   The compressible spring  48  initially urges the plug  43  into engagement with the shoulder  46 . However, as the internal thread  41  of the shield member  40  is threaded onto the external thread  28  of the plug  25 , the flat surface  44  of the plug  43  will abut the end face of the wall  25 A of the plug  25  in the area radially outside the shallow recess  25 B so that any forces developed during the engagement will not cause harmful mechanical stress to be applied to the Hall effect sensor  47  during assembly. A continued rotation of the shield member  40  to effect the aforesaid threaded engagement of the threads  28  and  41  will cause a relative axial movement of the shield member  40  toward the bottom wall of the steel cup  18  and a compression of the spring  48  until the shield member  40  abuts the surface of the bottom wall of the steel cup  18 . A continued rotation of the shield member  40  will cause an urging of the steel cup  18  toward the valve body (not illustrated) until the washer  15 B tightly abuts against a shoulder  21 B on the pole piece  21 . Thus, the single step of screwing the shield member  40  onto the threads  28  causes a proper orienting of the Hall effect sensor  47  with respect to the magnet  39  and a locking of the annular coil  14  in the proper position on the valve body and with respect to the pole pieces  21  and  22 . 
   A rubber o-ring  52  can, if desired, be provided between the shield member  40  and the bottom wall of the steel cup  18 . On the other hand, the rubber o-ring  52  can be replaced with a metal seal ring  52 A configured to wedge into contact with the shield member  40 , the bottom wall  19  of the steel cup  18  and the surface  23  of the pole piece  22  in order to optimize the magnetic shielding. In addition, a hollow or split steel ring  53  can be provided in the region of the crimped portion  27  of the pole piece  22  and configured to contact the pole piece  22  and the shield member  40  in order to enhance the magnetic shielding. The ring  53  does not need to completely encircle the aforesaid structure. 
   The Hall effect sensor  47  has a plurality of wires connected in a conventional way to it, and they extend through the synthetic resin plug  43  in a conventional way and exit the plug  43  in the form of a socket  53  having plural prongs  54  therein to which each respective wire is attached to facilitate the reception of a plug member (not illustrated) that can be received to connect the prongs to electrically conductive sockets provided on the plug. 
   The magnetic shielding for the aforesaid structure can be further enhanced by modifying the shield member  40  to include three components as shown in  FIG. 2 . More specifically, the modified shield member  40 B includes a steel shield member  40 C comparable to the steel shield member  40  described above and which has the internal thread  41  thereon. Surrounding the steel shield member  40 C is a non-magnetic material  40 D which in turn is surrounded by a further steel shield member  40 E. The non-magnetic material  40 D serves to isolate the steel shield member  40 C from the steel shield member  40 E. The modified shield member  40 B combined with the hollow or split steel ring  53  and the steel seal ring  52 A and the close tolerance fit of the steel shield member  40 B to the surface  23  on the pole piece  22  and the close tolerance fit of the surface  23  on the pole piece  22  in the hole  20  provides a very effective magnetic shield isolating the effects of the magnetic field from the operating coil on the Hall effect sensor  47 . 
   The shield member  40  is configured to shield the Hall effect sensor  47  from any significant electromagnetic field produced by said coil  14  during periods of activation causing rectilinear movement of the armature  29 . 
   Although a particular preferred embodiment of the invention has been disclosed in detail for illustrative purposes, it will be recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, lie with the scope of the present invention.