Patent Publication Number: US-8531259-B2

Title: Proportional electromagnet

Description:
BACKGROUND OF INVENTION 
     1. Field of Invention 
     The present invention relates to an electromagnet and, more particularly, to a proportional electromagnet. 
     2. Related Prior Art 
     An electromagnet is used for turning electricity into magnetism and often used where intermittent movement is desired. The electromagnet includes a coil around a metal core which includes a bore defined in an end. The bore jeopardizes the density of the magnetism. Therefore, the magnetism is not constant in an operative stroke. 
     Referring to  FIG. 4 , shown is a conventional electromagnetic apparatus  5  that includes a magnetic circuit. The magnetic circuit goes from a coil unit  51  into a magnetic shield via a first bushing  52 , a magnetic lining  53 , a first air gap  54 , a metal core  55 . Then, the magnetic circuit is divided into two branches. One of the branches goes into a second air gap  56 . The other branch goes into a supporting element  58  via a flange  57 . Then, the magnetic circuit returns into the coil unit  51  via a second bushing  59 . The bushings  52  and  59  and the air gaps  54  and  56  and the flange  57  are magnetic air gaps that exhibit a magnetic resistance about 400 to 800 times as high as magnetic metal about a same distance and area. Hence, an electromagnetic apparatus will operate inefficiently if includes many magnetic air gaps. 
     The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art. 
     SUMMARY OF INVENTION 
     It is an objective of the present invention to provide a proportional electromagnet for providing substantially constant magnetism during an operative stroke. 
     To achieve the foregoing objective, the proportional electromagnet includes a cylindrical shell, first and second covers connected to two ends of the shell by riveting, a metal core inserted through an axial defined in the second cover and formed with a first section located in the shell and a second section located outside the shell, a coil unit provided between the shell and the metal core, a supporting element provided on the first section of the metal core, a bushing provided on the second section of the metal core, a copper ring provided on the first section of the metal core to improve magnetic thrust of the proportional electromagnet, a stop provided on the first section of the metal core, and a magnetic shield provided between the first section of the metal core and the coil unit to direct magnetic flux toward the supporting element and the metal core to stably drive the metal core. 
     Other objectives, advantages and features of the present invention will be apparent from the following description referring to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention will be described via detailed illustration of the preferred embodiment versus prior art referring to the drawings wherein: 
         FIG. 1  is a cross-sectional view of a proportional electromagnet according to the preferred embodiment of the present invention; 
         FIG. 2  is a side view of a core of the proportional electromagnet shown in  FIG. 1 ; 
         FIG. 3  shows magnetism produced by the proportional electromagnet shown in  FIG. 1 ; and 
         FIG. 4  shows magnetism produced by a conventional electromagnet. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring to  FIGS. 1 and 2 , the proportional electromagnet includes a liner  21 , an iron core  2 , a base seat  3  and a coil unit  4  according to the preferred embodiment of the present invention. The bushing  1  is a cylindrical shell made of a sheet by rolling. Two covers, a bottom cover  11  and a top cover  12  respectively are secured to two ends of the bushing  1  by rivets for example. 
     The iron core  2  is inserted in the liner  21  and defines an aperture. The liner  21  includes a first end located outside the iron core  2  and a second end inserted in the bottom cover  11  and connected to the base seat  3 . Between the bushing  1  and the iron core  2  is provided the coil unit  4 . 
     A horn-shaped base seat  3  is connected to the second end of the liner  21  with a copper ring  22  and a stop  23 . The copper ring  22  acts to avoid magnetic leakage and improve proportional linearity of magnetic thrust of the proportional electromagnet. Between the bottom cover  11  and the top cover  12  is provided a flange functioning as a magnetic isolation ring or magnetic shield  24 . The iron core  2  and the base seat  3  are made of a same magnetic material or different magnetic materials. The liner  21  and the stop  23  are made of stainless steel that is non-magnetic. The flange  24  is made of copper. The stop  23  is used to control the shortest distance between the base seat  3  and the iron core  2  when they are attracted to each other because of magnetic excitement. 
     The present invention exhibits several advantageous features over the prior art. At first, subjected to a same electromotive force (“NI”), the present invention produces a magnetic circuit to provide a larger electromagnetic force than the prior art. Referring to  FIG. 3 , “A” stands for a non-magnetic metal magnetic circuit, “B” and “C” represent air gaps, and “D” refers to a magnetic metal magnetic circuit. The bushing  1 , the bottom cover  11 , the top cover  12 , and the flange  24 , in combination, define a sleeve. The magnetic circuit goes from the bottom cover  11  “D”, the liner  21  “A” and the iron core  2  “D”. Then, the magnetic circuit is divided into two branches. One of the branches goes axially through the air gap “B”. The other branch goes radially to the horn-shaped end of base seat  3  through the air gap “C”. Then, the magnetic circuit goes into the base seat  3  and the top cover  12  “D”. The air gaps B and C produce magnetic circuits that are necessary for the proportional function while there is only the non-magnetic magnetic circuit A. The area of the magnetic circuit is 4 times as large as that of the prior art. The proportion of the air gaps B and C is reduced, and the magnetic resistance of the air gaps B and C is also reduced. Hence, the present invention provides a larger electromagnetic force than the prior art. 
     Secondly, a conical surface is used instead of a conventional wedge-like surface. Therefore, the present invention can be made more easily than the prior art without jeopardizing the performance. 
     Thirdly, the liner  21  is directly secured to the base seat  3  by welding instead of the conventional caps that involve more difficult fabrication. 
     Fourthly, the present invention exhibits less magnetic resistance than the prior art because that the to cover  12  is in direct contact with the base seat  3 . 
     The present invention has been described via the detailed illustration of the preferred embodiment. Those skilled in the art can derive variations from the preferred embodiment without departing from the scope of the present invention. Therefore, the preferred embodiment shall not limit the scope of the present invention defined in the claims.