REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 12/484,422, filed Jun. 15, 2009, now U.S. Pat. No. 8,178,038, and claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 61/061,371, filed Jun. 13, 2008, entitled IMPROVED UNDERCUT CRANKSHAFT HARDENING COIL, the entireties of which applications are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present disclosure relates generally to the induction heating and more particularly to improved undercut crankshaft hardening coil apparatus and methods for hardening undercut crankshafts. 
     BACKGROUND 
     Modern large crankshafts for use in locomotives or other high torque applications are often undercut into the side wall, creating a recess. Although this offers an improved crankshaft for the application it presents a difficult challenge to properly heat treat the surface of the undercut. Descriptions of the undercut crankshaft hardening applications are found in U.S. Pat. Nos. 6,399,928 by Gezarzick et al and 7,145,115 by Zahn et al., which are incorporated herein by reference. Those disclosures required complex electrical connections and or coil configurations to engage both the undercut fillets and the journal to allow the part to be heated with one continuous process. 
     SUMMARY 
     One or more aspects of the disclosure are now summarized to facilitate a basic understanding of the disclosure, wherein this summary is not an extensive overview of the disclosure, and is intended neither to identify certain elements of the disclosure, nor to delineate the scope thereof. The primary purpose of the summary, rather, is to present some concepts of the disclosure in a simplified form prior to the more detailed description that is presented hereinafter. The present disclosure relates to improvements in induction heating coil assemblies and methods for induction hardening undercut fillets which may be employed for hardening crankshafts or other workpieces having recesses with undercut areas. The disclosed apparatus provides an active turn for heating a journal area in the workpiece recess and one or more passive turns which are translated toward undercut fillets after the coil assembly is moved toward the recess with coupling portions of the passive and active turns coupling energy from the active turn to the passive turn(s) for heating the undercut fillets. 
     In accordance with one or more aspects of the disclosure, an induction coil apparatus is provided, having a coil assembly comprised of an active turn and one or more passive turns. The active turn is coupleable to an electric power source to form a first conductive circuit including one or more active coupling sections and one or more crossover sections. When the assembly is located near a workpiece and energized, the crossover section(s) heat at least a portion of a journal area in a workpiece recess. The passive turn is electrically isolated from the active turn and forms a second conductive circuit including at least one passive coupling section and at least one passive heating section. The passive turn is translatable relative to the active turn between a first position for engaging with or disengaging from the workpiece in which the passive heating section clears a recess sidewall, and a second position in which the passive coupling section is proximate to and electromagnetically coupled with the active coupling section of the active turn and in which the passive heating section is located proximate to an undercut fillet area of the workpiece recess. In the second position, energy from the active turn is electromagnetically coupled to induce current in the passive turn(s) for fillet heating while the journal area is heated by the active turn. 
     In certain embodiments, the active turn includes a circumferential active heating portion proximate the journal area. 
     In certain embodiments, the passive turn is translatable relative to the active turn in a direction parallel to a longitudinal axis of the workpiece between the first and second positions. 
     In certain embodiments, an insulator is disposed between the passive coupling section and the active coupling section. 
     In certain embodiments, the passive heating section of the passive turn is located at least partially within the undercut fillet area of the workpiece recess in the second position. 
     Further aspects of the disclosure provide a method for hardening undercut fillets of a workpiece using induction heating. The method includes translating a coil assembly radially toward a recess in the workpiece such that a passive turn of the coil assembly clears a sidewall of the recess and at least one crossover section of an active coil of the coil assembly is proximate a journal area in the workpiece recess, translating the passive turn relative to the active turn such that a passive coupling section of the passive turn is proximate to and electromagnetically coupled with an active coupling section of the active turn and a passive heating section of the passive turn is located at least partially within an undercut fillet area of the workpiece recess, and energizing the active turn with electrical power to heat at least a portion of a journal area in the workpiece recess using the at least one crossover section of the active coil and to induce electrical current in the passive turn to heat at least a portion of the undercut fillet area of the workpiece recess using the passive heating section of the passive turn. In certain implementations, translation of the passive turn relative to the active turn comprises translating the passive turn in a direction parallel to a longitudinal axis of the workpiece. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following description and drawings set forth certain illustrative implementations of the disclosure in detail, which are indicative of several exemplary ways in which the principles of the disclosure may be carried out. The illustrated examples, however, are not exhaustive of the many possible embodiments of the disclosure. Other objects, advantages and novel features of the disclosure will be appreciated from the following detailed description of the disclosure when considered in conjunction with the drawings, in which: 
         FIGS. 1-4  are partial perspective, side and end elevation, and top plan views illustrating conductor portions of an exemplary coil assembly with an active turn and two passive turns in extended second positions in accordance with one or more aspects of the present disclosure; 
         FIG. 5  is a simplified end elevation view of the coil assembly of  FIGS. 1-4  illustrating the passive turns in first retracted positions for clearance during radial insertion to or extraction from a workpiece recess; 
         FIG. 6  is a simplified end elevation view of the coil assembly of  FIGS. 1-5  illustrating the passive turns in second extended positions for undercut fillet heating; 
         FIG. 7  is a simplified partial end elevation view of the coil assembly of  FIGS. 1-6  with the passive turns in first retracted positions illustrating insertion of the assembly into a recess of a crankshaft workpiece; 
         FIG. 8  is a simplified partial end elevation view of the coil assembly of  FIGS. 1-7  illustrating the passive turns axially extended to second positions for induction heating of the undercut fillet areas of the workpiece recess; 
         FIG. 9  is a simplified partial end elevation view of the coil assembly of  FIGS. 1-8  illustrating the position of an exemplary crossover portion of the active turn proximate a journal portion of the workpiece recess during induction heating; 
         FIGS. 10 and 11  are partial side and end elevation views of the coil assembly of  FIGS. 1-9  illustrating magnetic laminations installed for electromagnetic coupling and further details of an exemplary support structure; 
         FIG. 12  is a simplified end elevation view of another exemplary embodiment of the coil assembly with a single passive turn in a first retracted position for clearance during radial insertion to or extraction from a workpiece recess for heating single undercut fillets; 
         FIG. 13  is a simplified end elevation view of the coil assembly embodiment of  FIG. 12  illustrating the passive turn in a second extended position for undercut fillet heating; 
         FIG. 14  is a simplified partial end elevation view of the coil assembly of  FIGS. 12 and 13  with the passive turn in the first retracted position illustrating insertion of the assembly into a recess of a crankshaft workpiece; 
         FIG. 15  is a simplified partial end elevation view of the coil assembly embodiment of  FIGS. 12-14  illustrating the passive turn axially extended to a second position for induction heating of the undercut fillet area of the workpiece recess; 
         FIGS. 16 and 17  are partial end elevation views illustrating another coil assembly embodiment in which the passive turns are pivotally translatable between first retracted positions for insertion or removal and second extended positions for undercut fillet heating in accordance with the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the figures, several embodiments or implementations are hereinafter described in conjunction with the drawings, where like reference numerals are used to refer to like elements throughout, and where the various features are not necessarily drawn to scale. The present disclosure provides apparatus  2  and coil assemblies  4  thereof having an active turn  10  that couples with one or more fillet hardening passive turns  20 ,  21  and couples with a workpiece journal for hardening the journal  102  and also providing the energy to the two passive turns or coils to harden one or more undercut fillet areas  104  of the workpiece  100 . The disclosed approach advantageously locates the active turn crossovers  10   c ,  10   e  so as to inductively heat the journal  102 , and the active turn  10  can extend around a circumferential portion of the journal by up to about 180 degrees. The active turn  10 , moreover, is electrically connected to a power supply to conduct current from the supply for inductively heating the journal  102  via the crossovers. One or more inner passive turns  20 ,  21  are provided in at least one space within and/or below the active turn  10  in certain embodiments, where the passive turns  20 ,  21  are passively energized via electromagnetic coupling from the active turn  10  such that the passive turns  20 ,  21  are not connected to the power supply, where the passive turns  20 ,  21  each form a closed loop structure. A coupling portion  20   a ,  21   a  of each passive turn  20 ,  21  is proximate the circumferential and/or other coupling portion  10   b ,  10   f ,  10   d  of the active turn  10  so as to electromagnetically couple therewith, and a second portion  20   c ,  21   c  of the passive turn  20 ,  21  is extendable at least partially into an undercut of a fillet  104  for heating thereof. In certain journal portions  104  of a crankshaft workpiece  100  having two undercut fillets  104  at two axially spaced sides of the journal  102 , each side can have one or more passive heating turns or turn portions for heating the associated fillet  104 , with the passive turns  20 ,  21  of each side being axially movable at least partially into the undercut fillet areas  104  after radial approach of the coil arrangement  2  to or proximate the journal  102 . 
     Referring initially to  FIGS. 1-11 , an exemplary induction coil apparatus  2  is illustrated, which may be advantageously employed for hardening undercut fillets  104  of a crankshaft or other workpiece  100 . One embodiment is best shown in  FIGS. 1-4 , where the apparatus  2  has a coil assembly  4  including an active turn or coil  10  and two passive turns or coils  20  and  21 . The active turn  10  is coupleable using conductive couplings  11  and  12  to an electric power source to form a first conductive circuit therewith, where the active turn is formed of hollow copper tube structures to provide an internal fluidic path for circulation of coolant during operation via the couplings  11  and  12 . Likewise, the first and second passive turns  20  and  21  are formed of conductive (e.g., copper) tubes providing internal coolant passageways for coolant circulated via coolant couplings  40 . The active turn  10  of  FIGS. 1-11  is formed of sections  10   a - 10   g  including active coupling section  10   b , a first active crossover section  10   c , a second active coupling section  10   d , a second crossover section  10   e , another partial coupling portion  10   f  and a final portion  10   g , where the crossover sections  10   c  and  10   e  are operative to heat all or a portion of the workpiece journal area  102  in a recess  110  thereof when the coil assembly  4  is positioned at or near the workpiece  100 , as shown in  FIG. 9 . 
     The first passive turn  20  is electrically isolated from the active turn  10  and forms a closed conductive circuit including a circumferential coupling section  20   a , a crossover portion  20   b , a passive heating section  20   c , and a second crossover portion  20   d  connecting back to the coupling portion  20   a . Similarly, the second passive turn  21  forms a closed conductive circuit electrically isolated from the active turn  10  via coupling section  21   a , crossover sections  21   b  and  21   d  and an outlying heating section  21   c , and the passive turns  20  and  21  are separately cooled by fluid provided via tubes  40 . The active and passive turns  10 ,  20 , and  21  are fitted with lamination keeper structures  30  for laminations  42  ( FIGS. 10 and 11 ) for electromagnetic coupling of the active turn  10  with the passive turns  20  and  21 , where any suitable magnetic material may be used for the laminations  42 , such as iron in one embodiment. Other embodiments are possible using suitable magnetic material to form flux concentrator structures  42 , which need not be laminations. As shown in  FIGS. 10 and 11 , moreover, the coil apparatus  2  further includes protective outer covers  50  and may include other suitable mounting and support structures for translation operation as described herein. 
     Referring also to  FIGS. 5-9 , the passive turns  20  and  21  are translatable by any suitable mechanical translation devices (not shown) relative to the active turn  10  between a first position ( FIGS. 5 and 7 ) in which the passive heating sections  20   c  and  21   c  clear sidewalls  108  of a workpiece recess  110  as the coil assembly  4  is translated radially toward the recess  110  ( FIG. 7 ) and a second position ( FIGS. 6 and 8  in which the passive coupling sections  20   a ,  21   a  are proximate to and electromagnetically coupled with the first active coupling section  10   b ,  10   f ,  10   d  of the active turn  10 . As shown in  FIG. 8 , moreover, an insulator  26  may be provided in certain embodiments between the passive coupling section  20   a  and the active coupling section  10   b ,  10   f , as well as between the active coupling section  10   d  and the passive coupling section  21   a  of the second passive turn  21 , which may be any suitable insulator material, such as Teflon in one example. In the second positions, moreover, the first passive heating section  20   c  is located at least partially within a first undercut fillet area  104  of the workpiece recess  110 , and the second passive heating section  21   c  is located at least partially within a second undercut fillet area  104  of the workpiece recess  110 , as illustrated in  FIG. 8 . In addition, as shown in  FIG. 9 , the active turn crossover portions  10   c  and  10   e  are disposed to be proximate the workpiece journal portion  102  during induction heating when the apparatus  2  is translated toward the recess  110 . 
     In the embodiment of  FIG. 8 , the first passive turn  20  is translatable relative to the active turn  10  in a first direction (to the left in the figure) generally parallel to a longitudinal workpiece axis  8  between the first and second positions, and the second passive turn  21  is translatable in a generally opposite axial direction (to the right) between its first and second positions, where any suitable mechanism(s) can be used to provide the translation of the passive turns  20 ,  21  relative to the active turn  10 . 
     The current in the closely coupled fillet hardening active turns  20 ,  21  will be equal (except for leakage flux) and opposite to the current in the main active turn  10  in the illustrated embodiments. As a result, the current in the fillet hardening portions  20   c  and  21   c  is in the same direction as the main driving current of the active turn  10 , and the current induced in the fillets  104  is in the same direction as the main journal hardening current of the active turn crossover portions  10   c  and  10   e  so that the net electromagnetic configuration is that of a standard crankshaft hardening coil. With this arrangement, the fillet hardening passive sections  20   c  and  21   c  can be freely moved, at least partially, into and out of the fillet without any external electrical connection. As shown in  FIG. 11 , moreover, bumpers or guides  52  may be provided in the apparatus  2  for locating the apparatus  2  relative to a workpiece  100 , which will generally be rotated about the axis  8  during heating with the active turn  10  energized. In addition, the apparatus and the coil assembly  4  thereof may extend any circumferential distance about the workpiece  100 , such as about 180 degrees or less in various embodiments. 
     Referring now to  FIGS. 16 and 17 , the translation of the passive turns  20  and  21  need not be strictly parallel to the workpiece axis  8 . In the embodiment of  FIGS. 16 and 17 , the passive turns  20  and  21  are pivotally translatable between first retracted positions for insertion or removal of the apparatus  2  while clearing the sidewalls  108  ( FIG. 16 ), and second extended positions for undercut fillet heating ( FIG. 17 ). 
     Referring now to  FIGS. 12-15 , another exemplary embodiment of the coil assembly  4  is illustrated, having a single passive turn  20  configured generally as described above, along with an active turn  10  similar to that shown in the above figures, but with the section  10   d  being lowered to be proximate the journal  102 , such as approximately the same proximity as turn  20   c , in order to force the current to return through the journal  102 . This embodiment may be employed for hardening recesses  110  having only one undercut fillet  104 , which is heated via the translatable passive turn portion  20   c , while the journal  102  is heated via the active turn  10  as described in the above embodiments. 
     The above described apparatus  2  is particularly suitable for various induction heating processes. The disclosure provides an exemplary process for hardening undercut fillets  104  of a workpiece  100 , which may employ the described apparatus  2  or which may be used in conjunction with other apparatus. The process includes translating a coil assembly  4  radially toward a recess  110  in the workpiece  100  such that a passive turn  20  of the coil assembly  4  clears a sidewall  108  of the recess  110  and at least one crossover section  10   c ,  10   e  of an active coil  10  of the coil assembly  4  is proximate a journal area  102  in the workpiece recess  110 . The process also includes translating the passive turn  20  relative to the active turn  10  such that a passive coupling section  20   a  of the passive turn  20  is proximate to and electromagnetically coupled with an active coupling section  10   b ,  10   f  of the active turn  10  and a passive heating section  20   c  of the passive turn  20  is located at least partially within an undercut fillet area  104  of the workpiece recess  110 , and energizing the active turn  10  with electrical power to heat at least a portion of a journal area  102  in the workpiece recess  110  using the at least one crossover section  10   c ,  10   e  of the active coil  10  and to induce electrical current in the passive turn  20  to heat at least a portion of the undercut fillet area  104  of the workpiece recess  110  using the passive heating section  20   c  of the passive turn  20 . In certain embodiments, the translation of the passive turn  20  relative to the active turn  10  comprises translating the passive turn  20  in a direction parallel to a longitudinal axis  8  of the workpiece  100 . 
     The above examples are merely illustrative of several possible embodiments of various aspects of the present disclosure, where equivalent alterations and/or modifications will occur to others skilled in the art upon reading and understanding this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, systems, circuits, and the like), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component, such as hardware, software, or combinations thereof, which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the illustrated implementations of the disclosure. In addition, although a particular feature of the disclosure may have been illustrated and/or described with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Also, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in the detailed description and/or in the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”.
Improved induction heating methods are presented for induction hardening undercut fillets of crankshafts or other workpiece recesses or undercuts in which an active turn is energized to induce current in a passive turn translated toward a workpiece undercut for heating the undercut.