Abstract:
A rabbet joint between two components of an assembly eliminates the possibility of the formation of an undesirable radius between angled surfaces of the rabbet by segmenting the surfaces with recesses in an alternating pattern, thus forming the rabbet surfaces without sharp edges while still providing a sharp unobstructed inside-angle between the surfaces of the rabbet.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention pertains to a rabbet joint between two component parts and a method of forming a rabbet joint. More particularly, the present invention pertains to an apparatus and method for eliminating the radius commonly formed between the faces of an annular rabbet. 
     (2) Description of the Related Art 
     When joining components of an assembly, a rabbet is often useful on at least one of the components to provide a plurality of engagement surfaces between mating components of the assembly. In addition to providing structural support, rabbets also facilitate proper alignment of the components with respect to each other. 
     Typically, a rabbet takes the form of a right-angle groove or channel made into the edge of a component part that is adapted to receive and engage the corner of a mating component. As an example, rabbets are used to facilitate the assembly of components in dynamoelectric devices. Dynamoelectric devices are commonly comprised of, a rotor and shaft assembly, a stator encircling the rotor and shaft assembly, a cylindrical shell housing secured to and encircling the stator, and a pair of end shields secured to the ends of the housing. Because the end shields typically support bearings mounted on the rotor and shaft assembly and thereby position the rotor and shaft assembly relative to the stator, proper alignment of the end shields with respect to the housing can be critical to the operation of the dynamoelectric device. It is therefore common to provide a rabbet around the edge of the end shield to ensure that proper alignment with the housing is made. 
     A prior art end shield is shown in FIG.  1 . The end shield  10  has a hole  12  that allows a shaft of a dynamoelectric device to pass therethrough. An annular boss  14  extends around the hole  12  and is adapted to support a bearing mounted on the shaft. The end shield  10  also has a cylindrical rim  16  protruding from the perimeter of its main body and has a rabbet  18  formed thereon. Although end shields similar to the end shield  10  shown are common in the industry, many variations exist. For example, in FIG. 1 the end shield  10  is shown having a solid web  19  extending from the boss  14  to the rim  16 . However, it is also common to have a plurality of spokes extending radially from the boss  14  to the rim  16  with ventilation openings therebetween in place of the solid web  19 . Similarly, it is not necessary for an end shield to have a hole  12  for passage of the shaft therethrough, nor that the rim  16  extend axially from the main body. It is an improvement to the prior art annular rabbet  18  that is a focus of this invention. 
     The particular prior art rabbet  18  is formed on the rim  16  of the end shield  10 . The rabbet  18  is comprised of a cylindrical surface  20  and an adjacent, perpendicular annular surface  22 . The two surfaces form a right-angle shoulder around the rim  16  adapted to engage an end of a cylindrical shell housing of the dynamoelectric device. The diameter of the cylindrical surface  20  is approximately equal to that of a cylindrical interior surface of the housing nearest the housing end. Thus when the end shield  10  is assembled onto the housing, the cylindrical surface  20  engages the interior surface, thereby radially positioning and supporting the end shield  10  relative to the housing. Similarly, the annular surface  22  is designed to axially position the end shield  10  relative to the housing by engaging an annular end surface of the housing that is perpendicular to the interior surface of the housing. Once in proper alignment, the components may be further secured to each other by fasteners, adhesives, interlocking tabs or catches, or by other means for securing together components of an assembly as known to those skilled in the art. 
     As shown in the detailed cross-section of the prior art rabbet  18  in FIG. 2, a radius  24  is often inadvertently formed between the annular surface  22  and the cylindrical surface  20 . This radius  24  can be the result of cutting tool wear when a machining process is used to form the rabbet  18  on the end shield  10 . Additionally, the radius  24  may be the result of wear of the dies or molds used to cast or mold the end shields  10 . When precise alignment of the components within an assembly is required, any radius  24  formed between the annular surface  22  and the cylindrical surface  20  is undesirable in that, the radius  24  may prevent the annular surface  22  from engaging its mating component resulting in improper axial alignment of the components and the undesirable appearance of a gap between the end shield  10  and the shell housing. 
     Prior art solutions to this problem include reworking the end shield  10  by machining the rabbet  18  using sharp cutting tools to reduce the radius  24 . The extra machining process required by this solution greatly adds to the expense of production. Since the preferred method of fabrication is to mold or cast the end shields  10 , another solution has been to periodically rework or replace the molds or dies. This solution unnecessarily burdens the production process when the molds and dies are otherwise adequate. Yet another solution is to provide a chamfer or radius on the housing between the interior surface and the annular end surface of the housing that is larger than that of the radius  24 , thus providing relief in the housing for the radius  24  when the components are properly aligned. Like the other solutions, modifying the housing increases the cost of production and it is therefore desirable to find alternative solutions to the problem that can eliminate the radius  24  without adding a process step or otherwise increasing the cost of production. 
     The present invention overcomes the problems associated with prior art rabbet joints by utilizing a plurality of separated coplanar surfaces in place of the prior art annular surface  22  and by positioning a plurality of cylindrical surface segments perpendicular to and between the coplanar surfaces. The aggregate of the cylindrical surface segments replaces the cylindrical surface  20  of the prior art rabbet  18 . In accordance with this invention, no common edge is formed between the coplanar surfaces and adjacent cylindrical surface segments and, therefore, no radius  24  can be formed regardless of die, mold, or tool wear during the manufacturing process. This invention allows a component, such as an end shield, to be molded or cast with an annular rabbet type fitting and to align perfectly when assembled to a sharp edged mating component, regardless of minor die or mold wear. 
     SUMMARY OF THE INVENTION 
     The annular rabbet of the present invention replaces the prior art annular rabbet on an end shield. In accordance with the present invention, an end shield is formed with a plurality of cylindrical surface segments that are spaced circumferentially about a common axis by recesses in the end shield. Perpendicular and adjacent to the cylindrical surfaces are a plurality of spaced, coplanar surfaces with recesses therebetween. The coplanar surfaces are positioned circumferentially about the common axis between the cylindrical surface segments. The cylindrical surface segments and the coplanar surfaces are adapted to engage with an end of the cylindrical shell housing. The configuration of the cylindrical surface segments and the coplanar surfaces eliminates the mutual edge or corner formed between the cylindrical surface and the annular surface on prior art end shield rabbets. By eliminating such an edge on the present invention, an undesirable radius cannot be formed thereon. 
     In another aspect of the invention, a method of forming a rabbet joint between two component parts of an assembly comprises the steps of forming a plurality of cylindrical surface segments on a first component with the cylindrical surface segments being separated circumferentially about a common axis by recesses formed into the first component, forming a plurality of coplanar surfaces into the first component that are separated by recesses and are perpendicular to and between the cylindrical surface segments, and engaging the first component with the second component of the assembly. 
     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 isometric view of a prior art end shield of a dynamoelectric device having a rabbet thereon. 
     FIG. 2 is a partial cross-section of the prior art end shield rabbet of FIG.  1 . 
     FIG. 3 is a plan view of an end shield utilizing a rabbet of the preferred embodiment of the invention. 
     FIG. 4 is a partial isometric view of the end shield of FIG.  3 . 
     FIG. 5 is a partial cross-section of the end shield of FIG. 3 taken in the plane of line  5 — 5 . 
     FIG. 6 is a partial cross-section of the end shield of FIG. 3 taken in the plane of line  6 — 6 . 
     Reference characters in the written specification indicate corresponding parts throughout the several views of the drawings. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The preferred embodiment of the annular rabbet of the invention is used in conjunction with the end shield of a dynamoelectric device as shown in FIG.  3 . The end shield  30 , like the prior art end shield  10 , has a center hole  12  surrounded by a cylindrical boss  14  and a peripheral rim  16 . In the preferred embodiment, the rim  16  is cylindrical and has an inner surface  32  and a concentric outer surface  34  that extend axially from the main body of the end shield  30  and terminate at a perpendicular annular end surface  36 . 
     In the annular rabbet of the invention, as shown with greater detail in FIG. 4, a plurality of concentric cylindrical surface segments  38  are radially recessed into the rim  16  and are circumferentially spaced around the periphery of the rim  16 . The cylindrical surface segments  38  have the same radius of curvature and are circumferentially separated about their common axis by radial recesses  40  therebetween. Perpendicular to the cylindrical surface segments  38  are a plurality of arced coplanar surfaces  42  that extend radially into the rim  16  and are circumferentially spaced around the periphery of the rim  16 . The coplanar surfaces  42  are separated circumferentially about the common axis by axial recesses  44  and are positioned circumferentially between the cylindrical surface segments  38 . The cylindrical surface segments  38  of the preferred embodiment extend axially from the annular end surface  36  of the rim  16  and terminate at the recesses  44  that separate the coplanar surfaces  42 . Similarly, the coplanar surfaces extend radially inwards from the outer surface  34  of the rim  16  and terminate at the recesses  40  that separate the cylindrical surface segments  38 . The cylindrical surface segments  38 , like the prior art end shield cylindrical surface  20 , are dimensioned to engage the interior surface of a mating member such as the cylindrical shell housing, while the coplanar surfaces  42 , like the prior art annular surface  22 , are adapted to engage the annular end surface of the mating member. 
     The alternating positioning of the coplanar surfaces  42  circumferentially between the cylindrical surface segments  38  eliminates the possibility of the formation of a radius therebetween. The result is an unobstructed right-angle formed between the coplanar surfaces  42  and the cylindrical surface segments  38  as shown in the partial cross-sections of the preferred embodiment in FIGS. 5 and 6. Thus, although tool, die, or mold wear during production of components may result in variations of radii  46  between the cylindrical surface segments  38  and the recesses  44  and variations of radii  46  between the coplanar surfaces  42  and the recesses  40 , the radii  46  will not interfere with the engagement and desired relative positioning of the end shield  30  with the cylindrical shell housing of the dynamoelectric device. 
     It is important to understand that, although the preferred embodiment is shown with cylindrical surface segments  38  facing radially outward and the coplanar surfaces  42  extending radially inward from the outer surface  34  of the rim  16 , the cylindrical surface segments  38  could face radially inwards with the coplanar surfaces extending radially outwards from the inner surface  32  of the rim  16 . In such a situation, the cylindrical surface segments  38  would be adapted to engage an outer, rather than inner cylindrical surface of the mating component. Additionally, neither the inner surface  32  nor the outer surface  34  of the rim  16  need be cylindrical. The two surfaces could be formed along a straight edge of one component that meets with a straight edge of a second component. Furthermore, the cylindrical surface segments  38  and the coplanar surfaces  42  could be formed directly on the perimeter of the end shield  30  regardless of the presence of the rim  16 . 
     In accordance with the invention, a preferred method of forming a rabbet joint between a first component, for example an end shield, and a second component, for example a cylindrical shell housing, comprises the steps of, forming a plurality of cylindrical surface segments  38  on the first component separated circumferentially about their common axis by recesses  40 , forming a plurality of coplanar surfaces  42  separated by recesses  44  and annularly positioned perpendicular to and circumferentially between the cylindrical surface segments  38 , and engaging the first component with the second component. The steps of forming the coplanar surfaces  42  and the cylindrical surface segments  38  can be performed by molding, casting, machining, or by any method known by those skilled in the art. In the preferred embodiment the surfaces are cast. When engaging the components, the cylindrical surface segments  38  engage the cylindrical surface of the second component as the end shield  30  is moved axially onto the second component. The engagement of the cylindrical surface segments  38  with the cylindrical surface of the second components prevents radial movement of the first component relative to the second component. Final engagement occurs when the coplanar surfaces  42  engage with the second component to limit axial movement. In the preferred embodiment, the method is utilized with the first component being the end shield of a dynamoelectric device and the second component being the housing of the device. 
     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.