Patent Publication Number: US-6700234-B2

Title: Electromagnetic device

Description:
This application is based on Application No. 2000-327223, filed in Japan on Oct. 26, 2000, the contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electromagnetic device such as a stepping motor, a solenoid valve, or the like, used in an automotive continuously variable transmission, for example. 
     2. Description of the Related Art 
     FIG. 4 is an external view of a permanent-magnet stepping motor, FIG. 5 is a cross section taken along line V—V in FIG. 4, FIG. 6 is a cross section taken along line VI—VI in FIG. 5, FIG. 7 is a cross section taken along line VII—VII in FIG. 5, and FIG. 8 is a partial exploded perspective of the stepping motor in FIG.  5 . 
     In the figures, a permanent-magnet (PM) stepping motor  1 , which is immersed and used in an oil, includes: an outer casing  2  made of a resin; a tubular housing  12  made of a resin which is linked to the outer casing  2 ; a motor main body  3  disposed inside the outer casing  2 ; a shaft  4  functioning as a moveable shaft rotated by the motor main body  3 ; and a conversion mechanism  31  for converting rotation of the shaft  4  into rectilinear motion. Moreover, the outer casing  2  and the housing  12  constitute a cover. 
     The motor main body  3  includes a pair of stators  5  secured to the outer casing  2 , and a rotor  6  secured to the shaft  4 . The stators  5  have: coils  7  which are each constructed by winding a conducting wire in which an electrically-insulating layer is formed on a copper wire surface; coil terminals  8  led out from the coil  7 ; connector terminals  9  connected to the coil terminals  8 ; and an external connector  25  connected to the connector terminals  9 . The rotor  6  has a bush  10  secured to the shaft  4 , and a circumferentially-magnetized hollow cylindrical permanent magnet  11  fitted over and secured to the bush  10 . 
     The housing  12  is fastened to the outer casing  2  by a plurality of screws  12 A extending parallel to the shaft  4 . A circular interfitting aperture  2   a  is formed in the outer casing  2 , and an interfitting portion  12   a  for inserting into the interfitting aperture  2   a  is formed on the housing  12 . As shown in FIG. 6, three positioning projections  12   b , which protrude radially and come into contact with an inner circumferential surface of the interfitting aperture  2   a , are formed on an outer circumferential surface of the interfitting portion  12   a . Furthermore, an annular groove  12   c  is formed in a joining surface of the housing  12 , where the housing  12  joins the outer casing  2 . 
     A housing communicating aperture  12   d  communicating between internal and external portions of the housing  12  is disposed in a side surface portion of the housing  12 . A filter  13  for catching contaminants contained in the oil is disposed in the housing communicating aperture  12   d . The shaft  4  is rotatably held by a casing bearing  14  and a housing bearing  15 . The housing bearing  15 , which is secured inside the housing  12 , is a rubber-seal type. 
     A rod  16  reciprocated in an axial direction of the shaft  4  by rotation of the shaft  4  is disposed at a tip portion of the housing  12 . A base-end portion of the rod  16  is inserted inside the housing  12 , and a tip portion of the rod  16  protrudes from the tip portion of the housing  12 . A rod communicating aperture  16   a  communicating between the internal portion of the housing  12  and an internal portion of the rod  16  is formed in the rod  16 . A sleeve  17  for guiding rectilinear motion of the rod  16 , an oil seal  18  for preventing penetration of contaminants from an outer circumferential portion of the rod  16 , and a ring-shaped stopper  19  for regulating progression of the rod  16  are each secured to an inner circumferential surface of the tip portion of the housing  12 . 
     The conversion mechanism  31  includes a thread portion  4   a , a guide member  20  made of a resin which is formed in the base-end portion of the rod  16  and is engaged with the thread portion  4   a , and a stopper  21  made of a metal which is secured to the shaft  4  and regulates regression of the rod  16 . Stopper surfaces  20   b  and  21   a  which are perpendicular to the direction of rotation of the shaft  4  are formed on the guide member  20  and the stopper  21 , respectively. As shown in FIG. 7 a rotation-regulating projection portion  20   a  which protrudes radially and regulates rotation of the rod  16  is formed on an outer circumferential portion of the guide member  20 . Consequently, the guide member  20  is displaced in an axial direction of the shaft  4  by rotation of the shaft  4 . An operating member  22  made of a resin is mounted to the tip portion of the rod  16 . 
     A construction of each of the stators  5  will now be explained in detail with reference to FIGS. 9 to  12 . 
     As shown in FIG. 10, the coils  7  are each constructed by winding a conducting wire  50 , shown in FIG. 9, formed by coating a copper wire  51  with an electrically-insulating layer  52  composed of a polyimide resin, which is a thermoplastic resin, onto a bobbin  53  composed of nylon, which is a thermoplastic resin, for a predetermined number of winds. Then, end portions of the conducting wire  50  of each coil  7  are connected to the coil terminals  8  mounted to the bobbin  53 . Furthermore, as shown in FIG. 11, the coil  7  wound onto the bobbin  53  is embedded in an outer molding  54  composed of nylon, which is a thermoplastic resin. In addition, as shown in FIG. 12, cores  55  made of iron are disposed so as to surround the coil  7 , completing the construction of the stator  5 . 
     The stepping motor  1  constructed in this manner is mounted to an automobile continuously variable transmission, for example, and the operating member  22  attached to the tip portion of the rod  16  is engaged with a link  40  which opens and closes a transmission control valve in the continuously variable transmission. 
     When an electric current is passed through the external connector  25 , the coils  7  are magnetized, rotating the rotor  6  and the shaft  4  together. The guide member  20  is engaged in the thread portion  4   a  on the shaft  4 , and since rotation of the guide member  20  is regulated, rotation of the shaft  4  is converted into rectilinear motion of the guide member  20  and the rod  16 . 
     The transmission control valve is opened and closed through the link  40  by reciprocation of the rod  16 , ultimately changing the rotational velocity ratio between the drive shaft and the engine shaft. 
     The conventional stepping motor  1  is mounted to an automobile continuously variable transmission, for example, and is entirely immersed in the oil, which contains sulfur and organosulfur compounds. Furthermore, the coils  7  of the stators  5  are covered by the bobbins  53  and the outer moldings  54  which are composed of the thermoplastic resin, and the conducting wires  50  of the coils  7  are constructed by coating the copper wire  51  with the electrically-insulating layer  52 , which is composed of the thermoplastic resin. For that reason, the sulfur and the organosulfur compounds in the oil permeate the bobbins  53  and the outer moldings  54 , and in addition permeate the electrically-insulating layer  52 , reaching the copper wire  51 . As a result, chemical reactions occur at the surface of the copper wire  51  and organosulfur compounds are formed on the surface of the copper wire  51 , giving rise to a state of decreased adhesive strength of the electrically-insulating layer  52  to the copper wire  51 . 
     One problem has been that in this state, the electrically-insulating layer  52  may be breached due to interference between adjacent conducting wires  50  caused by repeated thermal expansion and thermal contraction due to the heat history of the conducting wires  50  themselves, leading to wire breakage or short circuiting between the conducting wires  50  caused by elution of copper due to electric potential differences between the conducting wires  50 . Another problem has been that breaching of the electrically-insulating layer  52  of the conducting wires  50  is more likely at positions where the conducting wires  50  and the bobbins  53 , which have different coefficients of thermal expansion, come into contact, leading to further short circuiting or wire breakage. 
     Yet another problem has been that when the temperature of the oil becomes greater than vaporization temperatures of volatile components in the oil due to heat generated by the coils  7 , the electrically-insulating layer  52  of the conducting wires  50  is more likely to be permeated by sulfur, etc., and there is a greater likelihood of short circuiting occurring between the conducting wires  50 . 
     SUMMARY OF THE INVENTION 
     The present invention aims to solve the above problems and an object of the present invention is to provide an electromagnetic device in which wire-breakage tolerance and short-circuiting tolerance of conducting wires are improved. 
     In order to achieve the above object, according to one aspect of the present invention, there is provided an electromotive device used in an oil, the electromagnetic device including: 
     an outer casing; 
     a moveable shaft supported by the outer casing; 
     a bobbin disposed inside the outer casing so as to be disposed around the moveable shaft on a common axis with the moveable shaft; and 
     a coil embedded in an outer molding, the coil being constructed by winding a conducting wire onto the bobbin, 
     wherein the bobbin and the outer molding are composed of an electrically-insulating material resistant to permeation by sulfur compounds. 
     According to another aspect of the present invention, there is provided an electromotive device used in an oil, the electromagnetic device including: 
     an outer casing; 
     a moveable shaft supported by the outer casing; 
     a bobbin disposed inside the outer casing so as to be disposed around the moveable shaft on a common axis with the moveable shaft; and 
     a coil embedded in an outer molding, the coil being constructed by winding a conducting wire onto the bobbin, 
     wherein the conducting wire is constituted by a copper wire, an electrically-insulating layer coated on the copper wire, and a protective layer coated on the electrically-insulating layer, the protective layer being composed of an electrically-insulating material resistant to permeation by sulfur compounds. 
     According to yet another aspect of the present invention, there is provided an electromotive device used in an oil, the electromagnetic device including: 
     an outer casing; 
     a moveable shaft supported by the outer casing; 
     a bobbin disposed inside the outer casing so as to be disposed around the moveable shaft on a common axis with the moveable shaft; and 
     a coil embedded in an outer molding, the coil being constructed by winding a conducting wire onto the bobbin, 
     wherein the conducting wire is constituted by a copper wire, a high-temperature solder layer coated on the copper wire, and a protective layer coated on the high-temperature solder layer, the protective layer being composed of an electrically-insulating material resistant to permeation by sulfur compounds. 
     The electrically-insulating material resistant to permeation by sulfur compounds may be a thermosetting resin. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features, objects and advantages of the present invention will become apparent from the following description of preferred embodiments with reference to the drawings in which like reference characters designate like or corresponding parts throughout several views, and in which: 
     FIG. 1 is a cross section showing a stepping motor according to Embodiment 1 of the present invention; 
     FIG. 2 is a cross section showing a conducting wire used in coils of a stepping motor according to Embodiment 2 of the present invention; 
     FIG. 3 is a cross section showing a conducting wire used in coils of a stepping motor according to Embodiment 3 of the present invention; 
     FIG. 4 is an external view of a conventional permanent-magnet stepping motor; 
     FIG. 5 is a cross section taken along line V—V in FIG. 4; 
     FIG. 6 is a cross section taken along line VI—VI in FIG. 5; 
     FIG. 7 is a cross section taken along line VII—VII in FIG. 5; 
     FIG. 8 is a partial exploded perspective of the stepping motor in FIG. 5; 
     FIG. 9 is a cross section showing a conducting wires used in coils of the stepping motor in FIG. 5; 
     FIG. 10 is a perspective showing a wound state of the coils in a stator of the stepping motor in FIG. 5; 
     FIG. 11 is a perspective showing a molded state of a resin portion in the stator of the stepping motor in FIG. 5; and 
     FIG. 12 is a perspective showing the stator of the stepping motor in FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention will now be explained with reference to the drawings. 
     Embodiment 1 
     FIG. 1 is a cross section showing a stepping motor according to Embodiment 1 of the present invention. Moreover, in the figure, portions which are the same as or correspond to those in the conventional stepping motor will be given the same numbering, and explanations thereof will be omitted. 
     In FIG. 1, coils  7  are each constructed by winding a conducting wire  50 , formed by coating a copper wire  51  with an electrically-insulating layer  52 , for a predetermined number of winds onto a bobbin  61  composed of an epoxy resin, which is a thermosetting resin functioning as an electrically-insulating material resistant to permeation by sulfur compounds. Then, end portions of the conducting wire  50  of each coil  7  are connected to coil terminals  8  mounted to the bobbin  61 . Furthermore, the coils  7  wound onto the bobbins  61  are each embedded in an outer molding  62  composed of an epoxy resin, which is a thermosetting resin. In addition, cores  55  made of iron are disposed so as to surround the coil  7 , constructing a stator  60 . Then, two stators  60  are disposed surrounding a shaft  4  on a common axis with the shaft  4 . 
     Moreover, the rest of the construction is the same as for the above conventional stepping motor  1 . 
     Now, considering molecular structure, in contrast to thermoplastic resins, which are aggregates of straight-chain macromolecules, thermosetting resins have a reticulate cross-linked structure. Thus, the permeation of sulfur and organosulfur compounds, etc., is extremely low in thermosetting resins compared to thermoplastic resins. 
     In a stepping motor  100 , which is an electromagnetic device constructed in this manner, because the coils  7  are embedded in the epoxy resin, which is a thermosetting resin, the amount of sulfur and the organosulfur compounds that permeate the bobbins  61  and the outer moldings  62  from the oil and reach the electrically-insulating layer  52  is significantly lowered. As a result, formation of sulfur compounds on a surface of the copper wire  51  resulting from chemical reactions between the sulfur and the copper wire  51  and between the organosulfur compounds and the copper wire  51  is suppressed, and reductions in adhesive strength of the electrically-insulating layer  52  to the copper wire  51  are suppressed. 
     Thus, even if there is interference between adjacent conducting wires  50  caused by repeated thermal expansion and thermal contraction due to the heat history of the conducting wires  50  themselves, damage to the electrically-insulating layer  52  is suppressed, and wire breakage and short circuiting between the conducting wires  50  caused by elution of copper due to electric potential differences between the conducting wires  50  are suppressed. 
     Furthermore, because damage to the electrically-insulating layer  52  of the conducting wire  50  at positions where the conducting wire  50  and the bobbins  61 , which have different coefficients of thermal expansion, come into contact, is also suppressed, short-circuiting tolerance and wire-breakage tolerance of the conducting wire  50  is improved. 
     In addition, even if the temperature of the oil becomes greater than vaporization temperatures of volatile components in the oil due to heat generated by the coils  7 , the likelihood of sulfur, etc., permeating the bobbins  61  and the outer moldings  62  and reaching the electrically-insulating layer  52  of the conducting wire  50  is reduced, ensuring the short-circuiting tolerance and the wire-breakage tolerance of the conducting wire  50 . 
     Embodiment 2 
     FIG. 2 is a cross section showing a conducting wire used in coils of a stepping motor according to Embodiment 2 of the present invention. 
     In FIG. 2, a conducting wire  63  is formed by additionally coating a protective layer  64  composed of epoxy resin, which is a thermosetting resin functioning as a electrically-insulating material resistant to permeation by the sulfur compounds, on the electrically-insulating layer  52  which is coated on the copper wire  51 . 
     Moreover, the construction of Embodiment 2 is the same as in Embodiment 1 except for the fact that the conducting wire  63  is used in place of the conducting wire  50 . 
     In Embodiment 2, because the protective layer  64 , which has low permeability to the sulfur and organosulfur compounds, is coated on the electrically-insulating layer  52 , the sulfur and organosulfur compounds permeating the bobbins  61  and the outer moldings  62  from the oil are blocked by the protective layer  64  from reaching the electrically-insulating layer  52 . 
     Thus, according to Embodiment 2, because the amount of the sulfur and organosulfur compounds reaching the electrically-insulating layer  52  is further reduced compared to Embodiment 1, the short-circuiting tolerance and the wire-breakage tolerance of the conducting wire  50  are still further improved. 
     Now, in Embodiment 2 above, the bobbins  61  and the outer moldings  62  used are composed of the epoxy resin, which is an electrically-insulating material resistant to permeation by the sulfur compounds, but bobbins and outer moldings composed of any thermoplastic resin may be used. In that case, even if the sulfur and organosulfur compounds in the oil permeate the bobbins  61  and the outer moldings  62 , because the sulfur and organosulfur compounds are blocked by the protective layer  64  from reaching the electrically-insulating layer  52 , the short-circuiting tolerance and the wire-breakage tolerance of the conducting wire are improved compared to the conventional example. 
     Embodiment 3 
     FIG. 3 is a cross section showing a conducting wire used in coils of a stepping motor according to Embodiment 3 of the present invention. 
     In FIG. 3, a conducting wire  65  is formed by coating a high-temperature solder layer  66  onto the copper wire  51 , and coating the protective layer  64  on the high-temperature solder layer  66 . Here, a lead-rich tin-lead solder having 90 wt % or more of lead is used for the high-temperature solder layer  66 . 
     Moreover, the construction of Embodiment 3 is the same as in Embodiment 1 except for the fact that the conducting wire  65  is used in place of the conducting wire  50 . 
     In Embodiment 3, because the protective layer  64 , which has low permeability to the sulfur and organosulfur compounds, is coated on the high-temperature solder layer  66 , the sulfur and organosulfur compounds permeating the bobbins  61  and the outer moldings  62  from the oil are suppressed by the protective layer  64  from reaching the high-temperature solder layer  66 . Then, any sulfur and organosulfur compounds which do permeate the protective layer  64  are prevented by the high-temperature solder layer  66  from reaching the copper wire  51 . Now, the high-temperature solder is less likely to react with the sulfur and organosulfur compounds than copper. Thus, sulfur compounds are not formed on the surface of the high-temperature solder layer  66  as a result of chemical reactions between the sulfur and organosulfur compounds and the high-temperature solder layer  66  and there is no decrease in adhesive strength of the protective layer  64  to the high-temperature solder layer  66 . As a result, the short-circuiting tolerance and the wire-breakage tolerance of the conducting wire  65  are still further improved. 
     Now, in Embodiment 3 above, the bobbins  61  and the outer moldings  62  used are composed of the epoxy resin, which is an electrically-insulating material resistant to permeation by the sulfur compounds, but bobbins and outer moldings composed of any thermoplastic resin may be used. In that case, even if the sulfur and organosulfur compounds in the oil permeate the bobbins  61  and the outer moldings  62 , because they are blocked by the protective layer  64  and the high-temperature solder layer  66  from reaching the copper wire  51 , the short-circuiting tolerance and the wire-breakage tolerance of the conducting wire are improved compared to the conventional example. 
     Moreover, each of the above embodiments has been explained using an epoxy resin, which is a material having low permeability to sulfur and organosulfur compounds, that is, an electrically-insulating material resistant to permeation by sulfur compounds, but any thermosetting resin may be used as an electrically-insulating material resistant to permeation by sulfur compounds, for example, a phenol resin. 
     Each of the above embodiments has been explained with reference to stepping motors, but the present invention is not limited to stepping motors; it may be applied to any electromagnetic device used in an oil, for example, to a solenoid valve for controlling the action of a transmission mechanism for adjusting the rotational velocity ratio between a drive shaft and an engine shaft by regulating an oil channel using a movable valve to control oil flow rate or pressure. 
     In Embodiment 3 above, the high-temperature solder layer  66  is formed using tin-lead solder having 90 wt % or more of lead, but it is not necessary for the lead content in the tin-lead solder to be 90 wt % or more; the lead content need only be 60 wt % or more. 
     Although the preferred embodiments of the present invention have been described above, it should be understood that the present invention is not limited thereto and that other modifications will be apparent to those skilled in the art without departing from the sprint of the invention. 
     The scope of the present invention, therefore, should be determined solely by the appended claims. 
     This electromotive device of the present invention is constituted as described above. Thus, this electromotive device has the following effects. 
     According to one aspect of the present invention, there is provided an electromotive device used in an oil, the electromagnetic device including: 
     an outer casing; 
     a moveable shaft supported by the outer casing; 
     a bobbin disposed inside the outer casing so as to be disposed around the moveable shaft on a common axis with the moveable shaft; and 
     a coil embedded in an outer molding, the coil being constructed by winding a conducting wire onto the bobbin, 
     wherein the bobbin and the outer molding are composed of an electrically-insulating material resistant to permeation by sulfur compounds, preventing wire breakage or short circuiting between conducting wires resulting from sulfur and organosulfur compounds in the oil permeating the bobbin and the outer molding and reaching the conducting wire, thereby providing an electromagnetic device enabling improved short-circuiting tolerance and wire-breakage tolerance in the conducting wire. 
     According to another aspect of the present invention, there is provided an electromotive device used in an oil, the electromagnetic device including: 
     an outer casing; 
     a moveable shaft supported by the outer casing; 
     a bobbin disposed inside the outer casing so as to be disposed around the moveable shaft on a common axis with the moveable shaft; and 
     a coil embedded in an outer molding, the coil being constructed by winding a conducting wire onto the bobbin, 
     wherein the conducting wire is constituted by a copper wire, an electrically-insulating layer coated on the copper wire, and a protective layer coated on the electrically-insulating layer, the protective layer being composed of an electrically-insulating material resistant to permeation by sulfur compounds, preventing wire breakage or short circuiting between conducting wires resulting from sulfur and organosulfur compounds in the oil permeating the bobbin and the outer molding and reaching the copper wire, thereby providing an electromagnetic device enabling improved short-circuiting tolerance and wire-breakage tolerance in the conducting wire. 
     According to yet another aspect of the present invention, there is provided an electromotive device used in an oil, the electromagnetic device including: 
     an outer casing; 
     a moveable shaft supported by the outer casing; 
     a bobbin disposed inside the outer casing so as to be disposed around the moveable shaft on a common axis with the moveable shaft; and 
     a coil embedded in an outer molding, the coil being constructed by winding a conducting wire onto the bobbin, 
     wherein the conducting wire being constituted by a copper wire, a high-temperature solder layer coated on the copper wire, and a protective layer coated on the high-temperature solder layer, the protective layer being composed of an electrically-insulating material resistant to permeation by sulfur compounds, preventing wire breakage or short circuiting between conducting wires resulting from sulfur and organosulfur compounds in the oil permeating the bobbin and the outer molding and reaching the copper wire, thereby providing an electromagnetic device enabling improved short-circuiting tolerance and wire-breakage tolerance in the conducting wire. 
     The electrically-insulating material resistant to permeation by sulfur compounds may be a thermosetting resin, facilitating formation of the bobbin, the outer molding, and the protective layer.