Patent Publication Number: US-9852865-B2

Title: Electrical switching arrangement with improved linear bearing

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of German Patent Application No. 102015212801.6, filed Jul. 8, 2015. 
     FIELD OF THE INVENTION 
     The invention relates to an electrical switch and, more particularly, to an electrical switch with a movable armature. 
     BACKGROUND 
     Electrical switches, such as relays, are known in the art. Patents U.S. Pat. No. 6,911,884 B2 and U.S. Pat. No. 8,138,863 B2 each disclose an electrical switch having a solenoid, a movable armature, an armature shaft attached to the movable armature, a contact assembly with a plurality of contacts, and other components. The contact assembly is located in a switching chamber region such that any electrical arcs which may arise can be sealed off from an electromagnetic drive system. The contact assembly is attached to the armature shaft, which penetrates a covering plate at a contact chamber aperture. The armature shaft is attached to the armature such that a movement of the armature is also transmitted to the contact assembly. 
     Due to mechanical tolerances in the overall design and contact wear from electrical arcs, the contacts of the contact assembly never touch corresponding mating contacts at the same time. Such a premature, one-sided mechanical contact initiates a force eccentric to the axis of a guide guiding motion of the armature. The spacing between the end of the armature shaft and the prematurely contacted contact acts as a lever, which tilts the guide. Since such an electrical switch is used to switch large loads, the contact forces for switching are high, leading to large radial forces transmitted by the lever to the guide. These forces can lead to wear on bearing surfaces of the guide or may even lead to the locking of the guide. 
     A locking of the guide can be avoided if the lever follows the condition (A/L)×2μ≦1, with A being the lever length, L the bearing length, and μ the friction factor. 
     Elongating the bearing length can prevent locking but impairs the shock resistance of the electrical switch. The contact chamber aperture can be used as a second bearing surface, however, this would require precise mechanical tolerances to avoid a lateral offset of the two bearing surfaces, which would lead to locking. 
     Locking may also be prevented by reducing the friction factor. However, reducing the friction factor is only possible to a limited extent and requires expensive bearing coatings such as polytetrafluoroethylene (PTFE). Furthermore, such a coating can become worn over the lifespan of the electrical switch, increasing the friction factor over time. 
     SUMMARY 
     The disclosed electrical switch comprises a solenoid assembly including a core casing having a first bearing site and a bearing bush having a second bearing site. The electrical switch also includes an armature movably borne in a switching direction at the first bearing site. The electrical switch further includes an armature shaft fixed to and movable with the armature and movably borne in the switching direction at the second bearing site. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described by way of example with reference to the accompanying figures, of which: 
         FIG. 1  is a sectional view of an electrical switch according to the invention; 
         FIG. 2  is a detail view of the electrical switch of  FIG. 1 ; and 
         FIG. 3  is a sectional view of the bearing bush of the electrical switch of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT(S) 
     The invention is explained in greater detail below with reference to embodiments of an electrical switch. This invention may, however, be embodied in other different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete and still fully convey the scope of the invention to those skilled in the art. 
     An electrical switch  1 , according to the invention, is shown in  FIGS. 1 and 2 . The electrical switch  1  has a solenoid assembly  3  and a contact chamber  5 . As shown in  FIG. 1 , the electrical switch  1  extends in a width b, which is measured along an x-axis, a depth t, which is measured along a y-axis, and a height h, which is measured along a z-axis. 
     The contact chamber  5 , as shown in  FIG. 1 , has an upper housing  7  and a contact chamber plate  11 , which together enclose an upper chamber  13 . The contact chamber plate  11  has a contact chamber aperture  9  located approximately centrally on the contact chamber plate  11 . 
     An armature shaft  15  extends into upper chamber  13  through contact chamber aperture  9 . Armature shaft  15  has a diameter d. 
     A contact plate  17  is affixed to an end  16  of armature shaft  15  within upper chamber  13 . Contact plate  17  has two armature contacts  19 . By moving armature shaft  15  in a switching direction S, armature contacts  19  can contact electrical contacts  21 , closing a current circuit. Electrical contacts  21  are connected to upper housing  7 . 
     The solenoid assembly  3 , as shown in  FIG. 1 , has a yoke  23  connected to the contact chamber plate  11 . The yoke  23  has, sectioned along a plane spanning in the x and the y direction, a U-shape which is open in the z direction. The yoke  23  has a floor  35  with a circular floor aperture  37 . Lateral walls  25  of yoke  23  enclose a solenoid  27 . 
     Solenoid  27  is rotationally symmetric relative to a central axis M, which is also the central axis M for armature shaft  15 . Solenoid  27  has a pancake coil  29 , which is rotationally symmetrical about central axis M. Solenoid  27  also has a solenoid wire  33  with loops  31  circumferentially coiled around pancake coil  29 . The loops  31  are symbolically represented in  FIG. 1  as a whole and not as individual loops. Pancake coil  29  bears against the contact chamber plate  11  in switching direction S and, counter to switching direction S, bears against floor  35  of the yoke  23 . 
     Solenoid  27  also has an inner space  39 . An armature  41  is entirely disposed within inner space  39  of solenoid  27 , while a core casing  43  is partially disposed within inner space  39  of solenoid  27 . Core casing  43  is formed of a magnetic material, such as pure iron with a galvanic coating of bronze or a Teflon-coated piece of pure iron. 
     An outer wall  45  of core casing  43  abuts an inner wall  47  of pancake coil  29 . A protrusion  49  of core casing  43  rests against the pancake coil  29  in the z direction, and, counter to the z direction, against floor  35  of yoke  23 . Both pancake coil  29  and core casing  32  are secured against movement in or counter to the z direction by yoke  23  and contact chamber plate  11 . 
     A lower end of the core casing  43  is received in the circular floor aperture  37 . The lower end of the core casing  43  has a casing chamfer  43   a  which is inclined relative to the central axis M. The lower end of core casing  43  is positioned outside of solenoid  27 , but does not project beyond yoke  23 , and thus is contained within the outer dimensions of solenoid assembly  3 . 
     Armature  41  and armature shaft  15  are rotationally symmetric about central axis M. Armature shaft  15  has a knurl  51 , . . . , The section of armature shaft  15  having knurl  51  is connected to armature  41  at an armature attachment  53 . In the shown embodiment, the armature attachment  53  is a laser weld, but one with ordinary skill in the art would understand that other attachments known in the art could be used as the armature attachment  53 . 
     Armature shaft  15  is disposed in inner space  39  of solenoid  27 , penetrates armature  41  at armature attachment  53 , and projects out of solenoid assembly  3  through contact chamber aperture  9 . In the shown embodiment, armature shaft  15  is made of a steel such as Cr—Ni steel, but one with ordinary skill in the art would understand that other materials, such as brass, are possible. Armature shaft  15  may have a rounded or angled cross-section. 
     Armature  41  has a cylindrical armature body  55  sealed by an armature floor  57  at an end situated counter to switching direction S. Armature floor  57  has a groove  60  extending annularly around central axis M. In the shown embodiment, groove  60  of armature floor  57  has a V-shaped cross-section, but groove  60  of armature floor  57  may alternatively have a rectangular or semicircular cross-section. Armature  41  also has an armature flange  59  positioned at an opposite end in switching direction S. In the shown embodiment, armature flange  59  is materially bonded to armature body  55 , but armature flange  59  may alternatively be integrally formed with armature body  55 . 
     Armature body  55  is partially surrounded by core casing  43  and is guided within core casing  43  in switching direction S over a bearing length L. Armature body  55  is guided and movably bears on a first bearing site  61  of core casing  43 , which forms a first bearing surface  62 . 
     Armature flange  59  is located in a cavity  63  formed by pancake coil  29  and contact chamber plate  11 . Cavity  63  has a height h and armature flange  59  has a flange height hF. Flange height hF is measured in switching direction S from the position at which armature flange  59  abuts pancake coil  29  up to a portion of armature  41  which projects furthest in the switching direction S. 
     Armature shaft  15  is fixed to armature  41  and extends from armature floor  57  through cavity  63 . Armature shaft  15  is surrounded by a spring  67  such that the spring  67  abuts both armature floor  57  and a side of contact chamber plate  11  which points counter to the switching direction S. 
     At an end of solenoid assembly  3  opposite contact chamber  5 , a bearing element  68  in the form of a bearing bush  69  is inserted and form-fit into core casing  43 . The bearing bush  69  is shown in  FIGS. 1 and 3 , and is made of a plastic material. 
     Bearing bush  69  has an inner bearing section  71 , an outer bearing section  73 , and an annular disc  75  connecting inner bearing section  71  and outer bearing section  73 . Inner bearing section  71 , outer bearing section  73 , and annular disc  75  are symmetrical about central axis M and are connected to one another by material bonding at a side of bearing bush  69  counter to the switching direction S. Bearing bush  69  also has an annular trench  77  formed between inner bearing section  71  and outer bearing section  73 . 
     Bearing bush  69  has a bearing flange  76 . In the shown embodiment, bearing flange  76  is monolithically formed with annular disc  75 , but the bearing flange  76  could alternatively be attached to annular disc  75 . Bearing bush  69  may be formed by injection-molding or by other forms of production known to those with ordinary skill in the art. 
     Bearing flange  76  extends away from the central axis M, projecting past outer bearing section  73 . Bearing flange  76  abuts an end of core casing  43  facing counter to switching direction S and prevents bearing bush  69  from being inserted deeper into core casing  43 . Bearing flange  76  has a bearing chamfer  76   a  complementary to casing chamfer  43   a,  such that casing chamfer  43   a  abuts bearing chamfer  76   a  along a surface inclined away from central axis M. In the shown embodiment, both bearing chamfer  76   a  and casing chamfer  43   a  have a 45° angle. 
     Bearing bush  69 , as shown best in  FIG. 3 , has a cylindrical receiving aperture  79  which tapers at insertion slopes  81 . This taper represents an annular step  82  which protrudes inwards from the inner bearing section  71  to the central axis M. Annular step  82  forms a bush bearing surface  82   a,  which acts as a second bearing site  83  having a length  91 . Second bearing site  83  is not centered in bearing bush  69 , but rather is arranged offset in bearing bush  69  in switching direction S, i.e. toward the interior of solenoid assembly  3 . Second bearing site  83  is spaced apart from first bearing site  61 . 
     Armature shaft  15  is received in and movably bears on second bearing site  83 . A length of second bearing site  83  in switching direction S is at most half of a diameter of armature shaft  15 . Insertion slopes  81  simplify the introduction of armature shaft  15  into bearing bush  69  by centering armature shaft  15  with respect to bearing bush  69 . 
     The assembly and use of electrical switch  1  will now be described with reference to  FIGS. 1 and 2 . 
     Contact chamber  5  forms a cover  6  which is attached to and seals off solenoid assembly  3 . Cover  6  may be attached to solenoid assembly  3  by welding, gluing, screwing, riveting, or other forms of fastening known to those with ordinary skill in the art. Cover  6  separates solenoid assembly  3  from armature contacts  19 , shielding solenoid assembly  3  from electrical arcs. Contact chamber aperture  9  is the sole connection between solenoid assembly  3  and upper chamber  13 . 
       FIG. 1  shows electrical switch  1  in an open position  0 , in which spring  67  is not prestressed or is only slightly prestressed.  FIG. 2  shows electrical switch  1  in a contact position K. Contact position K represents the first mechanical contact between contact plate  17  and electrical contacts  21 . In contact position K, armature  41  and armature shaft  15  have been moved by the magnetic field of solenoid  27  in switching direction S. During movement, armature  41  bears on first bearing site  61 , while armature shaft  15  bears on second bearing site  83 . Since second bearing site  83  is narrow, friction on armature shaft  15  is reduced. A stroke H of the electrical switch  1  in the transition from open position O to contact position K is the difference between height h and flange height hF. 
     The movement of armature  41  and armature shaft  15  is transmitted to contact plate  17 . As shown in contact position K in  FIG. 2 , a first armature contact  19   a  does not touch a first electrical contact  21   a,  while a second armature contact  19   b  does touch a second electrical contact  21   b.  Between the first electrical contact  21   a  and the first armature contact  19   a,  a gap  85  must be overcome before the mechanical contact is made. Gap  85  may arise from contact plate  17  being tilted or by first armature contact  19   a  being affected by burnout, for example from electrical arcs, such that first armature contact  19   a  has been shortened. This tilting cannot be wholly avoided by electrical switch  1 , but is minimized by the armature  15  bearing on both first bearing site  61  and second bearing site  83 . The spacing between first bearing site  61  and second bearing site  83  increases a bearing length of armature shaft  15  to resist higher tilting moments. 
     The initial mechanical touching of the contact plate  17  with second electrical contact  21   b  leads to the transverse force F, which is transmitted from the magnetic field of solenoid  27  to armature  41  and armature shaft  15 , acting on contact plate  17  along a direction counter to switching direction S. Transverse force F is transmitted over a lever length A onto armature shaft  15 , tilting armature  41  within core casing  43 . Lever length A is measured from central axis M to second armature contact  19   b.  Since the second armature contact  19   b  bears against the second electrical contact  21   b  over a large area, a mechanical point of application  19   c  is located centrally on the second armature contact  19   b  in the x-direction. 
     Advantageously, the electrical switch  1  according to the present invention, due to the first bearing site  61  and the second bearing site  83 , resists tilting and locking of the armature shaft  15  without reducing shock resistance or requiring a costly bearing coating.