Abstract:
A dynamoelectric device utilizes retaining members to prevent the windings from migrating into the air-gap between the stator and the rotor. The retaining members used in the device are axially self-locking, thereby preventing undesired axial translation of the retaining members during severe operating conditions of the dynamoelectric device.

Description:
BACKGROUND OF THE INVENTION 
     (1). Field of the Invention 
     This invention pertains to the field of dynamoelectric devices such as electric motors and generators that are used to convert energy in either electrical or mechanical form into the other. More particularly, this invention pertains to the use of a self-locking retaining member, frequently referred to as a top stick, positioned between stator poles to prevent windings from entering the air gap between the stator and rotor. The use of self locking retaining members increases the safety and reliability of dynamoelectric devices by preventing undesirable axial translation of retaining members that may occur during severe operating conditions of dynamoelectric devices. 
     (2). Description of the Related Art 
     There are numerous types of dynamoelectric devices in the prior art. A typical dynamoelectric device of the prior art in represented generally by the numeral  20  as shown in cross-section in FIG.  1 . In general, the dynamoelectric device is comprised of a rotor  22  that is revolvable about an axis  24 , a plurality of stator poles  26  positioned circumferentially about the rotor  22 , and windings  28 . A slot  30  extending in the direction of the axis  24  is formed between every two immediately adjacent stator poles  26 , as is more clearly shown in detail in FIG.  2 . The windings  28  consist of at least one electrically conductive coated wire wound within the slots  30  about one or more of the stator poles  26 . 
     Typically, a slot liner  32  is positioned between the windings  28  and the stator poles  26  within the slots  30  to prevent the windings  28  from directly contacting the stator poles  26 . The slot liners  32  are generally rectangular insulating sheets made of polymeric or fibrous material and have two opposite ends  33 , the first end  33  positioned adjacent one of the two stator poles  26  that defines the slot  30  and the second end  33  positioned adjacent the other stator pole  26 . Additionally, a liner cap  34  made of material similar to the slot liner  32 , commonly referred to as a wedge, may extend from the first end  33  of the slot liner  32  to the second end  33 , thereby covering the inner most surface of the windings  28 . By “inner” and “inwardly”, what is meant is, radially inward toward the axis  24  of the rotor  22 . 
     A failure mode of such prior art devices arises when the windings  28  migrate from between stator poles  26  radially inward into the air gap  36  between the rotor  22  and stator poles  26 , interfering with the moving rotor assembly. This failure occurs frequently in devices with large slot fills or large slot openings between stator poles wherein typical wire retention methods are insufficient. This is often a concern in switched reluctance motors that are subject to high winding temperatures or vibration loads. Recently, this failure mode has become an increasing concern when utilizing switched reluctance motors in safety critical applications such as in the automotive steering industry. 
     In those prior art devices having liner caps  34 , they are generally radially non-rigid and therefore unable to prevent radial migration of the windings  28 . One method utilized in prior art devices to prevent winding migration has been to varnish the windings, thereby preventing the wire passes that comprise the winding from moving independently of one another. This method has been shown to be beneficial in preventing winding migration but not at elevated winding temperatures. At elevated winding temperatures, the varnish strength is reduced and the varnish may therefore be unable to prevent winding migration. Additionally, the varnishing process typically has a considerably lengthy cycle time and high burden cost during production of dynamoelectric devices. 
     To reduce the cycle time and burden cost associated with the varnishing method, a similar method of preventing the wire passes that comprise the winding from moving independently of one another has been to utilize bondable wire coatings. This method, as is the case with the varnish method, is beneficial in preventing winding migration but not at elevated winding temperatures. 
     To prevent winding migration inherent to both the varnish and bondable wire coating methods at elevated temperatures, retaining members, commonly referred to as top sticks, have been developed in the prior art to provide a barrier between the windings  28  and the air gap  36  between the stator and rotor. This method is typically used as a secondary restraint in conjunction with other retention methods such as utilizing a bondable coating on the windings  28 . Prior art retaining members are generally rectangular members that are slid axially into the slots between stator poles during assembly of the dynamoelectric devices. A typical prior art retaining member  38  is shown in FIGS. 3-5. The top stick retaining member  38  is shown in a plan view in FIG. 3 with its radially inner side shown. The retaining member is shown in cross section in FIG.  4 . FIG. 5 is a partial view of the retaining member in one operative environment assembled in a dynamoelectric device between a pair of adjacent stator poles  26  and retaining a winding  28  between the poles. 
     The prior art retaining member  38  is formed of a generally rigid material that provides a barrier in the slot  30  between the windings  28  and the air gap  36 . As can be seen in FIGS. 4 and 5, the prior art retaining member  38  has a radially inner surface  40  that faces inwardly toward the rotor and has a width slightly less than that of the slot  30  inwhich it is positioned. The inner surface  40  is often slightly curved, matching the radius of the inward most surfaces of the stator poles  26  so as to maintain a uniform air gap  36  between the rotor  22  and stator poles  26 . The T-shaped cross section of the main body of the retaining member  38  as seen in FIG. 4 provides the main body with side rails  42  that are slightly farther apart than the narrowest portion of the width of the slot  30 . The rails  42  engage with inner edges  43  of the pair of adjacent stator poles to hold the retaining member  38  radially in the slot. Thus, when an inward force is applied to the prior art retaining member, the side rails  42  prevent the prior art retaining member  38  from translating inward by engaging both the stator poles  26  that define the slot  30 . 
     In addition to the main body, prior art retaining members  38  have also been provided with end stops  44  positioned at one axial end of the retaining member  38 . The end stops  44  project outwardly beyond the width of the retaining member&#39;s inner surface  40  as seen in FIG.  4  and therefore are unable to fit within the slot  30  between adjacent stator poles  26 . During installation into a dynamoelectric device, the end of the retaining member  38  axially opposite the end stops  44  is inserted axially into the slot  30 . The configuration of the retaining member  38  allows it to slide axially between the inner edges  43  of the adjacent stator poles  26  until the end stops  44  engage the stator poles  26  or another axially rigid portion of the device. Thereafter, the end stops  44  prevent axial over insertion of the retaining member  38 , thereby increasing the ease of their installation. 
     Retaining members are advantageous over other prior art solutions in that, when properly axially aligned, they effectively prevent excessive winding migration toward the gap  36  between the stator and rotor while maintaining a low burden cost during production. However, a disadvantage associated with such prior art retaining members has been an undesired axial movement of the retaining members as a result of severe three dimensional vibration and thermal expansion and contraction of the stator poles relative to the retaining member during the life of the dynamoelectric device. In prior art devices which utilize the varnish method in combination with retaining members  38 , axial movement of the retaining members is limited slightly by the varnish if the retaining member is installed prior to the varnishing process. In prior art devices which utilize the bondable wire coating method, prior art retaining members  38  do not have any means other than friction against the inner edges  43  of the adjacent stator poles  26 , windings  28 , or against the liner cap  34  that prevents them from axially translating in a direction opposite to the direction in which they were inserted and tend to back-out in such severe situations. Additionally, the amount of friction is often minimized to ease assembly of the retaining member. The axial migration of the prior art retaining members can result in a portion of the windings entering the air gap between the rotor and stator or ultimately contacting the rotor assembly, thereby decreasing the performance or life of the device. Axial migration of the retaining members may also result in undesired interference of the retaining members with other rotating parts located on the rotor assembly. 
     The present invention overcomes the disadvantages associated with the use of prior art retaining members by providing a locking mechanism on the retaining members so as to prevent their undesired axial movement. The invention provides reliable operation of dynamoelectric devices without the need for costly varnishing and without adding additional components to prior art devices already utilizing retaining members. 
     SUMMARY OF THE INVENTION 
     The retaining members of the present invention are designed to be used in place of conventional retaining members. In accordance with the dynamoelectric device of the invention and the method of axially locking retaining members within a dynamoelectric device in accordance with this invention, a locking mechanism is provided on the retaining member. When the retaining member is in its proper position, the locking mechanism engages a restraining portion of the dynamoelectric device so as prevent undesired axially translation of the retaining member. 
     In general, the dynamoelectric device of the present invention comprises a rotor having an axis of rotation, a plurality of stator poles and windings positioned circumferentially about the rotor, and self-locking retaining members. The windings and retaining members are located within the slots formed between the stator poles, with the retaining member being nearest the rotor so as to act as a barrier between the windings and the rotor. A locking mechanism is provided on each retaining member preventing undesired axial migration of the member. 
     In another aspect of the present invention, a method for preventing windings from entering the air gap between a stator and rotor of a dynamoelectric device comprises axially sliding a retaining member into a slot between two stator poles. When the proper axial position of the retaining member is reached, it is automatically axially locked in place and is radially positioned between the windings and the rotor so as to prevent winding migration into the air gap. 
     While the principle advantages and features of the present invention have been described above, a more complete and thorough understanding of the invention may be attained by referring to the drawings and detailed description of the preferred embodiments, which follow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an end view, in section, of a prior art dynamoelectric device. 
     FIG. 2 is a detailed partial view, in section, of a prior art dynamoelectric device showing a single slot. 
     FIG. 3 is a plan view of a prior art retaining member. 
     FIG. 4 is a view, in section, of the prior art retaining member along the line  4 — 4  of FIG.  3 . 
     FIG. 5 is an isometric view of the prior art retaining member installed in a dynamoelectric device. 
     FIG. 6 is a plan view of the preferred embodiment of the retaining member of the invention. 
     FIG. 7 a detailed partial view, in section, of the tab of the preferred embodiment taken along the line  7 — 7  of FIG.  6 . 
     FIG. 8 is a detailed partial view of the preferred embodiment installed in a dynamoelectric device. For clarity purposes, the windings are not shown. 
     FIG. 9 is a partial isometric view, in detail, showing the preferred embodiment of the invention in a dynamoelectric assembly. 
     FIG. 10 is a fragmented plan view of an alternative embodiment retaining member of the invention. 
     FIG. 11 is a fragmented plan view of another alternative embodiment of the retaining member of the invention. 
     FIG. 12 is a fragmented plan view of another alternative embodiment of the retaining member of the invention. 
     FIG. 13 is a detailed partial view, in section, of the retaining member of FIG. 12 taken along the line  13 — 13  of FIG.  12 . 
     References characters in the written specification indicate corresponding parts throughout the several views of the drawings. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The embodiments of the retaining member used in the present invention are similar to prior art retaining members. The embodiments incorporate the general T-shaped cross section, the slightly curved inner surface  40 , side rails  42  that engage with the inner edges  43  of the adjacent stator poles  26 , and end stops  44  of the prior art retaining members  38  described in detail in the discussion of the background of the invention. For that reason, these aspects of the invention are given the same reference numbers in the Figures and their description is not repeated in this section. 
     Unlike the prior art retaining members  38 , the preferred embodiment, shown as retaining member  46  in FIG. 6, utilizes an additional locking mechanism in the form of a tab  48 . The tab  48  as shown in detail in FIG. 7, is generally thinner and narrower than the main body of the retaining member  46  so as to allow it to easily deflect when a radial force is directly applied to the tab  48 . As can be seen from the detail of the tab  48  in FIG. 7, a wedge shaped protrusion  50  extends radially outward from the end of the tab  48 . The wedge shaped protrusion  50  has a sloped surface  52  nearest the end of the tab  48  and a locking surface  54  adjacent thereto. 
     The preferred embodiment of the retaining member  46  of the invention is adapted to be inserted into a position completely closing the slot  30  by axially sliding it into place between the inner edges  43  of the two adjacent stator poles  26 . When the retaining member  46  is being axially translated, the sloped surface  52  of the tab  48  could contact a portion of the dynamoelectric device, for example the windings  28  or the liner cap  34 , which would exert an inward radial force on the tab  48 . This force would cause the tab  48  to deflect and axially pass over that portion of the device that engaged the sloped surface  52  of the tab  48  without preventing further axial translation of the retaining member  46 . When the retaining member  46  is in its proper position covering the stator slot, the tab  48  is, at least partially, in its original undeflected position. The tab is designed to engage with an existing portion of the dynamoelectric device, for example the end turns of the windings  28 , the liner cap or wedge  34 , or an end cap that covers the winding end turns (not shown). The sloped surface  52  of the tab allows the tab to flex and pass over the portion of the device with the resiliency of the tab causing the tab to snap back to its original orientation bringing the locking surface  54  into engagement with the portion of the device. This snapping of the tab  48  over the portion of the device prevents or limits axial translation of the retaining member  46  in the opposite direction to that of its insertion by the locking surface  54  of the tab  48  engaging with the portion of the device when such translation occurs. In the preferred embodiment of the invention, the restraining portion of the of the dynamoelectric device is the edge of the liner cap  34  as shown in FIG.  8 . However, as set forth above, the retaining member  46  could just as easily utilize another portion of the device such as an edge of a housing cover or the edge of the windings. Each of the portions of the dynamoelectric device with which the tab  48  can engage and lock against are intended to be represented schematically in FIG. 9 as portion  56 . 
     It is important to understand that while the preferred embodiment of the invention is described as having a wedged shaped protrusion  50  with a sloped surface  52  that deflects the tab  48  during insertion of the retaining member  46 , the wedge shaped protrusion  50  and sloped surface  52  could just as easily deflect the restraining portion of the dynamoelectric device rather than the tab  38  and achieve similar results. For example, the windings  28  or liner cap  34  could deflect as the retaining member  46  is inserted and then engage with the locking surface  54  of the tab  48 . Finally, the locking mechanism tab  48  could engage with a portion of the dynamoelectric device and also prevent further axial translation in the direction of installation, thereby eliminating the need for the end stops  44 . This could be accomplished by the tab engaging in a complementary slot in the device, thereby preventing movement of the retaining member in both axial directions. 
     An alternative of the preferred embodiment is shown in FIG.  10 . The retaining member  58  is shown having two tabs  60  that deflect towards each other rather than radially. This embodiment utilizes similar wedge shaped protrusions that deflect against the stator poles  26  as the retaining member  58  is slid axially into the assembly. Once the retaining member  58  is in its proper position, the tabs  60  deflect back away from each other over the edges of the stator poles  26 . Thus, in this alternative embodiment of the retaining member  58 , the stator poles  26  act as the corresponding restraining portion of the dynamoelectric device. This embodiment of the invention could just as easily have only one tab  60  and function equivalently. 
     Another alternative embodiment is shown in FIG.  11 . This retaining member  62  utilizes one or more barbs  64  that act as the locking mechanism. The barbs  64  extend from the side rails  42  to engage the stator poles  26  in an interference fit, or engage in recessed slots in the sides of the poles. The wedge shape of the barbs  64  allows the retaining member  62  to axially translate more easily during installation and they resist axial translation in the opposite direction. 
     Yet another alternative embodiment of the retaining member  48  is shown in FIGS. 12 and 13. This retaining member  66  utilizes two wedge shaped protrusions  68  that project radially inward from the side rails  42 . During installation of the retaining member  66 , the protrusions  68  engage the surface the stator poles  26  that is normally in contact with the side rails  42 . This contact forces the entire retaining member to deflect the liner cap  34  or the windings  28 . Just as the retaining member  66  reaches its proper axial position, the protrusions  68  pass over the edge of the stator poles  26  and the liner cap  34  or windings  28  force the side rails  42  against the stator poles  26 . Once in position, the wedge shape of the protrusions  68  prevent the retaining member from translation axially in the opposite direction by engaging the sides of the stator poles  26 . 
     In accordance with the invention, the preferred method of manufacturing a dynamoelectric device as shown in FIGS. 6-9 comprises the step of inserting a retaining member  46  into the device by axially sliding it into one of the slots between two inner edges  43  of adjacent stator poles  26 . The insertion is continued until the end stops  44  engage the stator poles  26  preventing further insertion and the locking mechanism tab  48  or one of its alternate embodiments engages with a portion of the dynamoelectric device as described above. When the retaining member is in its proper position, axial translation in the opposite direction is prevented by the locking surface  54  of the wedge shape protrusion  50  on the tab  48  engaging the portion of the dynamoelectric device. The preferred method of manufacturing the dynamoelectric assembly is not limited to the use of the retaining member shown in FIGS. 6-9 and could also be practiced using retaining members similar to those shown in FIGS. 10-13 or their equivalents as described above. 
     While the present invention has been described by reference to specific embodiments, it should be understood that modifications and variations of the invention may be constructed without departing from the scope of the invention defined in the following claims.