Abstract:
An improved method for forming a vehicle wheel includes the steps of steps of: (a) providing a wheel rim defining a rim axis and including a generally axially extending well portion and a pair of opposed ends, one of the ends including an inboard tire bead seat retaining flange and an inboard tire bead seat, and the other end including an outboard tire bead seat; (b) providing a generally circular wheel disc blank defining a disc axis, the disc blank including an inner annular wheel mounting portion and an outer annular portion; (c) subjecting the wheel disc blank to a series of metal forming operations to produce a finished disc having a final profile, the finished wheel disc having an outer annular portion, an inner annular wheel mounting portion, and an intermediate portion having a generally convex profile; and (d) joining the finished wheel disc to the wheel rim to produce a fabricated vehicle wheel.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates in general to vehicle wheels and in particular to an improved method for producing a fabricated vehicle wheel. 
     A conventional fabricated vehicle wheel is typically of a two-piece construction and includes an inner disc and an outer “full” rim. The disc can be cast, forged, or fabricated from steel, aluminum, or other alloys, and includes an inner annular wheel mounting portion and an outer annular portion. The wheel mounting portion defines an inboard mounting surface and includes a center pilot or hub hole, and a plurality of lug receiving holes formed therethrough for mounting the wheel to an axle of the vehicle. The rim is fabricated from steel, aluminum, or other alloys, and includes an inboard tire bead seat retaining flange, an inboard tire bead seat, an axially extending well, an outboard tire bead seat, and an outboard tire bead seat retaining flange. In some instances, a threepiece wheel construction having a mounting cup secured to the disc is used. In both types of constructions, the outer annular portion of the disc is secured to the rim by welding. 
     A full face fabricated wheel is distinguished from other types of fabricated wheels by having a one-piece wheel disc construction. In particular, the full face wheel includes a “full face” disc and a “partial” rim. The full face disc can be formed cast, forged, or fabricated from steel, aluminum, or other alloys. The full face disc includes an inner annular wheel mounting portion and an outer annular portion which defines at least a portion of an outboard tire bead seat retaining flange of the wheel. The wheel mounting portion defines an inboard mounting surface and includes a center pilot or hub hole, and a plurality of lug receiving holes formed therethrough for mounting the wheel to an axle of the vehicle. The partial rim is fabricated from steel, aluminum, or other alloys, and includes an inboard tire bead seat retaining flange, an inboard tire bead seat, an axially extending well, and an outboard tire bead seat. In some instances, the outboard tire bead seat of the rim and the outer annular portion of the disc cooperate to form the outboard tire bead seat retaining flange of the full face wheel. In both types of constructions, the outboard tire bead seat of the rim is positioned adjacent the outer annular portion of the disc and a weld is applied to secure the rim and the disc together. 
     SUMMARY OF THE INVENTION 
     This invention relates to an improved method for forming a vehicle wheel and includes the steps of: (a) providing a wheel rim defining a rim axis and including a generally axially extending well portion and a pair of opposed ends, one of the ends including an inboard tire bead seat retaining flange and an inboard tire bead seat, and the other end including an outboard tire bead seat; (b) providing a generally circular wheel disc blank defining a disc axis, the disc blank including an inner annular wheel mounting portion and an outer annular portion; (c) subjecting the wheel disc blank to a series of metal forming operations to produce a finished disc having a final profile, the finished wheel disc having an outer annular portion, an inner annular wheel mounting portion, and an intermediate portion having a generally convex profile; and (d) joining the finished wheel disc to the wheel rim to produce a fabricated vehicle wheel. 
     Other advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram illustrating a prior art sequence of steps for producing a prior art full face fabricated steel vehicle wheel. 
     FIG. 2 is a cross sectional view of a disc blank for use in producing the prior art fabricated steel vehicle wheel. 
     FIG. 3 is a cross sectional view showing the initial stamping of the disc blank into a generally bowl shaped wheel disc. 
     FIG. 4 is a cross sectional view showing the intermediate stamping of the bowl shaped disc to produce a partially formed wheel disc. 
     FIG. 5 is a cross sectional view showing the forming of the windows in the partially formed wheel disc. 
     FIG. 6 is a cross sectional view showing the trimming of the outer diameter of the partially formed wheel disc. 
     FIG. 7 is a cross sectional view showing the forming of the hub hole and lug bolt mounting holes in the partially formed wheel disc. 
     FIG. 8 is a cross sectional view showing the final stamping of the partially formed wheel disc to produce a finished prior art full face fabricated steel wheel disc. 
     FIG. 9 is a sectional view of a prior art full face fabricated steel vehicle wheel. 
     FIG. 10 is a block diagram illustrating a sequence of steps for producing a prior art full face fabricated aluminum vehicle wheel. 
     FIG. 11 is a cross sectional view of the disc blank for use in producing the prior art full face fabricated aluminum vehicle wheel. 
     FIG. 12 is a cross sectional view showing the initial stamping of the disc blank into a generally salad bowl shaped wheel disc. 
     FIG. 13 is a cross sectional view showing the intermediate stamping of the salad bowl shaped disc to produce a partially formed wheel disc. 
     FIG. 14 is a cross sectional view showing the intermediate stamping and the forming of the hub hole in the partially formed wheel disc. 
     FIG. 15 is a cross sectional view showing the forming of the windows in the partially formed wheel disc. 
     FIG. 16 is a cross sectional view showing the coining of the back side of the windows and the restriking of the hub hole in the partially formed wheel disc. 
     FIG. 17 is a cross sectional view showing the forming of the lug bolt mounting holes, the restriking of the wheel disc, and the flow spinning of the partially formed wheel disc in order to produce a finished prior art full face fabricated aluminum wheel disc. 
     FIG. 18 is a sectional view of the prior art full face fabricated aluminum vehicle wheel. 
     FIG. 19 is a block diagram illustrating a sequence of steps for producing a full face fabricated steel vehicle wheel in accordance with the present invention. 
     FIG. 20 is a cross sectional view of a disc blank for use in producing the full face fabricated steel vehicle wheel in accordance with this invention. 
     FIG. 21 is a cross sectional view showing the initial stamping of the disc blank into a generally bulge bowl shaped wheel disc in accordance with this invention. 
     FIG. 22 is a cross sectional view showing the intermediate stamping of the bulge bowl shaped wheel disc to produce a partially formed disc in accordance with this invention. 
     FIG. 23 is a cross sectional view showing the forming of the windows in the partially formed wheel disc in accordance with this invention. 
     FIG. 24 is a cross sectional view showing the trimming of the outer diameter of the partially formed wheel disc in accordance with this invention. 
     FIG. 25 is a cross sectional view showing the forming of the hub hole and lug bolt mounting holes in the partially formed wheel disc in accordance with this invention. 
     FIG. 26 is a cross sectional view showing the final stamping of the partially formed wheel disc to produce a finished full face fabricated steel wheel disc in accordance with this invention. 
     FIG. 27 is a partial sectional view showing the generally bulge bowl shaped wheel disc formed during the initial stamping operation. 
     FIG. 28 is a partial sectional view showing the partially formed wheel disc after the intermediate stamping operation. 
     FIG. 29 is a sectional view of a full face fabricated steel vehicle wheel in produced in accordance with this invention. 
     FIG. 30 is a block diagram illustrating a sequence of steps for producing a full face fabricated aluminum vehicle wheel in accordance with the present invention. 
     FIG. 31 is a cross sectional view of the disc blank for use in producing the full face fabricated aluminum vehicle wheel in accordance with this invention. 
     FIG. 32 is a cross sectional view showing the initial stamping of the disc blank into a partially formed wheel disc in accordance with this invention. 
     FIG. 33 is a cross sectional view showing the intermediate stamping of the wheel disc to produce a partially formed wheel disc having a generally bulge bowl shape in accordance with this invention. 
     FIG. 34 is a cross sectional view showing the intermediate stamping and the forming of the hub hole in the partially formed wheel disc in accordance with this invention. 
     FIG. 35 is a cross sectional view showing the forming of the windows in the partially formed wheel disc in accordance with this invention. 
     FIG. 36 is a cross sectional view showing the coining of the back side of the windows and the restriking of the hub hole in the partially formed wheel disc in accordance with this invention. 
     FIG. 37 is a cross sectional view showing the forming of the lug bolt mounting holes, the restriking of the wheel disc, and the flow spinning of the partially formed wheel disc in order to produce a finished full face fabricated aluminum wheel disc in accordance with this invention. 
     FIG. 38 is a sectional view of a fill face fabricated aluminum wheel produced in accordance with this invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, FIG. 1 illustrates a block diagram showing a prior art sequence of steps for producing a fill face fabricated steel vehicle wheel, indicated generally at  60  in FIG.  9 . Initially, in step  10 , a flat sheet of steel material (not shown) is formed into a disc blank  30 , shown in FIG.  2 . The disc blank defines a generally uniform disc thickness T. Following this, the disc blank  30  is initially stamped in step  12  to produce a generally bowl shaped disc  32 , shown in FIG.  3 . The bowl-shaped disc  32  includes an outer annular portion  34 , an inner annular wheel mounting portion  36  having a “flattened” bottom, and an intermediate portion  37  having a generally concave profile. In particular, during the initial stamping operation of step  12 , the disc blank  30  is stamped to define a first predetermined axial distance A defined between an inner surface  34 A of the outer annular portion  34  and an inner surface  36 A of the inner mounting portion  36 . Alternatively, in step  12 , the disc blank  30  can be stamped to produce an intermediate portion  37  having a generally straight profile (not shown). 
     The bowl-shaped disc  32  is then stamped into a partially formed disc  38  having a predetermined profile, shown in FIG. 4, during step  14 . Next, during step  16 , a plurality of windows  40  (only one window illustrated in FIG. 5) are formed in the disc  38  to produce a partially formed disc  42 . Following this, the windows  40  are coined and an outer edge of the partially formed disc  42  is trimmed to a predetermined diameter during step  18  to produce a partially formed disc  44  shown in FIG.  6 . Next, in step  20 , a center hub hole  46  and a plurality of lug bolt mounting holes  48  (only one hole  48  is illustrated) are formed in the disc  44  to produce a partially formed disc  50  shown in FIG.  7 . Following this, the partially formed disc  50  is restriked and then subjected to a final stamping operation during step  22  to produce a finished full face steel wheel disc  52  shown in FIG.  8 . During step  22 , a second predetermined axial distance B is defined between an inner surface  54 A of an outer annular portion  54  of the disc  50  and an inner surface  56 A of an inner mounting portion  56  of the disc  52 . In the illustrated embodiment, the second predetermined axial distance B is less than the first predetermined axial distance A. Alternatively, the second predetermined axial distance B can be equal to the first predetermined axial distance A. Following this, the full face disc  52  is secured to a partial steel wheel rim  59  during step  24  to produce the finished full face fabricated steel vehicle wheel  60  shown in FIG.  9 . Thus, in a conventional prior art steel full face wheel disc application, the initial stamping operation of step  12  is operative to form a bowl-shaped disc  32  having a finished part “tread” depth (i.e., axial distances A and B are the same) or deeper (i.e., axial distance A greater than axial distance B). Also, in a conventional prior art steel full face wheel disc application the initial stamping operation of step  12  is operative to form a bowl-shaped disc  32  wherein the intermediate portion  37  has a generally concave bowl wall surface (as shown in FIG.  3 ), or alternatively, a generally straight bowl wall surface (not shown). 
     Referring now to FIG. 10, there is illustrated a block diagram showing a prior art sequence of steps for producing a full face fabricated aluminum vehicle wheel, indicated generally at  110  in FIG.  18 . Initially, in step  60 , a flat sheet of aluminum material (not shown) is formed into a disc blank  80 , shown in FIG.  11 . The disc blank  80  defines a generally uniform disc thickness Z. Following this, the disc blank  80  is initially stamped in step  62  to produce a generally “salad” bowl-shaped disc  82 , shown in FIG.  12 . The salad bowl-shaped disc  82  includes an outer annular portion  84 , an inner annular portion  86 , and an intermediate portion  87  having a generally concave profile. In particular, during the initial stamping operation of step  62 , a first predetermined axial distance C is defined between an inner surface  84 A of the outer annular portion  84  and an inner is surface  86 A of the inner annular portion  86  of the disc  82 . Alternatively, in step  62 , the intermediate portion  87  can have a generally straight profile (not shown). 
     The salad bowl-shaped disc  82  is then stamped into a partially formed disc  88  having a predetermined profile, as shown in FIG. 13, during step  64 . The partially formed disc  88  includes an inner annular wheel mounting portion  90  having a “flattened” bottom. During step  64 , a predetermined second axial distance D is defined between the inner surface  84 A of the outer annular portion  84  and an inner surface  90 A of the inner annular wheel mounting portion  90 . As illustrated, the second predetermined axial distance D is less than the first predetermined axial distance C. Alternatively, during step  62 , a slight flattening of the inner annular portion  86  can occur. However, it is not possible to flatten the inner annular portion  86  of the aluminum blank  80  to the shape shown in FIG. 3 when using a steel blank  30 . 
     Next, during step  66 , the partially formed wheel disc  88  is subjected to a further stamping operation and a center hub hole  92  is formed in the wheel disc  88  to produce a partially formed wheel disc  94  shown in FIG.  14 . Following this, a plurality of windows  96  (only one window is illustrated in FIG. 15) are formed in the partially formed disc  94  during step  68  to produce a partially formed wheel disc  98 . In step  70 , the windows  96  are coined and the wheel disc  98  is restriked to produce a partially formed wheel disc  100  shown in FIG.  16 . 
     Next, in step  72 , a plurality of lug bolt mounting holes  102  (only one hole  102  is illustrated in FIG. 17) are formed in the wheel disc  100 , the wheel disc  100  is restriked, and then the wheel disc  100  is preferably subjected to a final flow spinning operation to produce a finished full face aluminum wheel disc  104  shown in FIG.  17 . In particular, during the restriking operation of step  72 , a predetermined third axial distance E is defined between an inner surface  106 A of an outer annular portion  106  and the inner surface  90 A of the inner mounting portion  90 . In the illustrated embodiment, the predetermined third axial distance E is less than the predetermined second axial distance D. Alternatively, the second axial distance D and the third axial distance E can be generally equal to one another. Also, during the flow spinning step  72 , a slight thinning of the material may occur (not shown). The radially outwardly extending outer annular end portion  106  of the wheel disc  104  defines the outboard tire bead seat retaining flange of the full face fabricated vehicle wheel  110 . 
     Next, in optional step  74 , an outer end portion  108  of the outboard tire bead seat retaining flange  106  is subjected to a trimming operation to provide a smooth tire flange radius. Alternatively, the disc wheel  102  may be subjected to a final stamping operation in step  72  instead of the flow spinning operation. When the disc  102  is subjected to a final stamping operation in step  72 , the trimming operation of optional step  74  is usually performed. 
     Following this, the finished fill face aluminum wheel disc  104  is secured to a partial aluminum wheel rim  130 , shown in FIG. 18, having a predetermined shape in step  76 . As shown therein, the wheel rim  130  includes an inboard tire bead seat retaining flange  132 , an inboard tire bead seat  134 , a generally axially extending well  136 , and an outboard tire bead seat  138 . In particular, during step  76 , the outboard tire bead seat  138  of the rim  130  is positioned adjacent the outboard tire bead seat retaining flange  106  of the disc  104 , and a circumferentially extending continuous, air-tight weld  140  is applied to secure the wheel rim  130  and wheel disc  104  together to produce the finished full face fabricated aluminum vehicle wheel  110 . 
     Referring now to FIG. 19, there is illustrated a block diagram showing a sequence of steps for producing a first embodiment of a fabricated vehicle wheel in accordance with the present invention. The vehicle wheel produced according to this sequence of steps is illustrated as being a full face fabricated steel vehicle wheel, indicated generally at  278  in FIG.  29 . However, it will be appreciated that the present invention can be used in conjunction with other types of fabricated vehicle wheels having a steel wheel disc. For example, the vehicle wheel can be a “bead seat attached” wheel (such as shown in FIG. 4 of U.S. Pat. No. 5,188,429 to Heck et al.), a “well attached” wheel (such as shown in FIG. 3 of Heck et al.), or a “modular wheel” construction including a “partial” rim and a full face wheel disc (such as shown in U.S. Pat. No. 5,360,261 to Archibald et al.), all of these patents incorporated herein by reference. 
     Turning to FIG. 19, the sequence of steps for producing the full face fabricated steel vehicle wheel  278  of the present invention will be discussed. Initially, in step  200 , a flat sheet of steel material (not shown) is formed into a disc blank  230 , shown in FIG.  20 . The disc blank  230  defines a generally uniform disc thickness T 1 . Following this, the disc blank  80  is initially stamped in step  202  to produce a generally “bulge” bowl shaped wheel disc  232 , shown in FIGS. 21 and 28. The bulge bowl shaped wheel disc  232  includes an outer annular portion  234 , an inner annular wheel mounting portion  236  having a flattened bottom, and an intermediate portion  238  having a generally convex profile. In particular, during the initial stamping operation of step  202 , the disc blank  230  is engaged by a plurality of dies, six dies  280 ,  282 ,  284 ,  286 ,  288 , and  290  being illustrated in FIG.  27 . During step  202 , a first predetermined axial distance F is defined between an inner surface  234 A of the outer annular portion  234  and an inner surface  236 A of the inner annular portion  236 . As will be discussed below, by forming the disc  232  with a shallower generally convex shaped bowl, as compared to the depth and shape of the prior art steel bowl  32  shown in prior art FIG. 3, a smaller blank  230  can be used compared to the size of the prior art blank  30 . 
     The bulge bowl shaped disc  232  is then stamped into a partially formed is wheel disc  240  having a predetermined profile, as shown in FIGS. 22 and 28, during step  204 . In particular, during step  204 , the bulge bowl shaped disc  232  is engaged by a plurality of dies, ten dies  292 ,  294 ,  296 ,  298 ,  300 ,  302 ,  304 ,  306 ,  308 , and  310  being illustrated in FIG.  28 . The wheel disc  240  includes an outer annular portion  242 , an inner annular wheel mounting portion  244 , and an intermediate portion  246  having a generally convex profile. Also, during step  204 , a predetermined second axial distance G is defined between an inner surface  242 A of the outer annular portion  242  and an inner surface  244 A of the inner annular wheel mounting portion  244 . As illustrated, the second predetermined axial distance G is greater than the first predetermined axial distance F. As will be discussed below, the second predetermined axial distance G is preferably a finished part “tread” depth. 
     Next, during step  206 , a plurality of windows  248  (only one window illustrated in FIG. 23) are formed in the wheel disc  240  to produce a partially formed disc  250 . Following this, in step  208 , the windows  248  are coined and an outer edge of the partially formed disc  250  is trimmed to a predetermined diameter during step  208  to produce a partially formed wheel disc  252  shown in FIG.  24 . Next, in step  210 , a center hub hole  254  and a plurality of lug bolt mounting holes  256  (only one hole  256  is illustrated in FIG. 25) are formed in the disc  252  to produce a partially formed disc  258  as shown in FIG.  25 . Following this, the partially formed disc  258  is restriked and then subjected to a final stamping operation during step  212  to produce a finished full face steel wheel disc  260  shown in FIG.  26 . Following this, the full face steel wheel disc  260  is secured to a partial steel wheel rim, indicated generally at  270  in FIG. 29, during step  214  to produce the finished full face fabricated steel vehicle wheel  278  shown in FIG. 29 of the present invention. As shown in FIG. 29, the wheel rim  270  defines a generally horizontal or longitudinal axis X and the inner surface  244 A of the inner annular wheel mounting portion  244  of the wheel disc  260  defines a generally vertical axis Y which is generally perpendicular to the rim axis X. 
     Referring now to FIG. 30, there is illustrated a block diagram showing a sequence of steps for producing a second embodiment of a fabricated vehicle wheel in accordance with the present invention. The vehicle wheel produced according to this sequence of steps is illustrated as being a full face fabricated aluminum vehicle wheel, indicated generally at  480  in FIG.  38 . However, it will be appreciated that the present invention can be used in conjunction with other types of fabricated vehicle wheels having an aluminum wheel disc. For example, the vehicle wheel can be a “bead seat attached” wheel (such as shown in FIG. 4 of U.S. Patent No. 5,188,429 to Heck et al.), a “well attached” wheel (such as shown in FIG. 3 of Heck et al.), a “bimetal” wheel construction including an aluminum disc and a steel rim (such as shown in U.S. Pat. No. 5,421,642 to Archibald), or a “modular wheel” construction including a “partial” rim and a fill face wheel disc (such as shown in U.S. Pat. No. 5,360,261 to Archibald et al.), all of these patents incorporated herein by reference. 
     Turning now to FIG. 30, the sequence of steps for producing the full face fabricated aluminum vehicle wheel  480  of the present invention will be discussed. Initially, in step  400 , a flat sheet of aluminum material (not shown) is formed into a disc blank  420  as shown in FIG.  31 . The disc blank  420  defines a generally uniform disc thickness T 2 . Following this, the disc blank  420  is initially stamped in step  402  to produce a generally straight bowl shaped wheel disc  422 , shown in FIG.  32 . The straight bowl shaped wheel disc  422  includes an outer annular portion  424 , an inner annular portion  426  having a curved bottom, and an intermediate portion  428  having a generally straight profile. During step  402 , a first predetermined axial distance H is defined between an inner surface  424 A of the outer annular portion  424  and an inner surface  426 A of the inner annular portion  426 . Following this, in step  404 , the wheel disc  42  is then is stamped into a partially formed wheel disc  430  having a predetermined profile, as shown in FIG.  33 . The partially formed wheel disc  430  includes an outer annular portion  432 , an inner annular wheel mounting portion  434 , and an intermediate portion  436  having a generally convex profile. Also, during step  402 , the predetermined axial distance H is maintained between an inner surface  432 A of the outer annular portion  432  and an inner surface  434 A of the inner annular wheel mounting portion  434 . Alternatively, in step  402 , the intermediate portion  428  can be formed with a generally convex profile and/or the axial distance H between surfaces  424 A and  426 A can be less than the axial distance H between surfaces  432 A and  434 A in a manner similar to that described above in connection with FIGS. 21 and 22. 
     Next, during step  402 , the partially formed wheel disc  430  is subjected to one or more stamping operations and a center hub hole  438  is formed in the wheel disc  430  to produce a partially formed wheel disc  440  shown in FIG.  34 . Following this, a plurality of windows  442  (only one window  442  is illustrated in FIG. 35) are formed in the partially formed disc  440  during step  408  to produce a partially formed wheel disc  444 . In step  410 , the windows  442  are coined and the wheel disc  444  is restriked to produce a partially formed wheel disc  446  shown in FIG.  36 . 
     In step  412 , a plurality of lug bolt mounting holes  448  (only one hole  448  is illustrated in FIG. 37) are formed in the wheel disc  446 , the wheel disc  446  is restriked, and then the wheel disc  446  is preferably subjected to a final flow spinning operation to produce a finished full face aluminum wheel disc  450  shown in FIG.  37 . The wheel disc  450  includes a generally radially outwardly extending outer annular end portion  452  which defines the outboard tire bead seat retaining flange of the full face fabricated vehicle wheel  480 . 
     Next, in optional step  41 , an outer end portion  454  of the outboard tire bead seat retaining flange  452  is subjected to a trimming operation to provide a smooth tire flange radius. Alternatively, the disc wheel  446  may be subjected to a final stamping operation in step  412  instead of the flow spinning operation. When the disc  446  is subjected to a final stamping operation in step  412 , the trimming operation of optional step  414  is usually performed. 
     Following this, the finished full face aluminum wheel disc  450  is secured to a partial aluminum wheel rim  470 , shown in FIG. 38, having a predetermined shape in step  416 . As shown therein, the wheel rim  470  includes an inboard tire bead seat retaining flange  472 , an inboard tire bead seat  474 , a generally axially extending well  476 , and an outboard tire bead seat  478 . In particular, during step  416 , the outboard tire bead seat  438  of the wheel rim  470  is positioned adjacent the outboard tire bead seat retaining flange  452  of the wheel disc  450 , and a circumferentially extending continuous, air-tight weld  482  is applied to secure the wheel rim  470  and wheel disc  450  together to produce the finished full face fabricated aluminum vehicle wheel  480  of the present invention. As shown in FIG. 38, the wheel rim  470  defines a generally horizontal or longitudinal axis XI and the inner surface  434 A of the inner annular wheel mounting portion  434  of the wheel disc  450  defines a generally vertical axis Y 1  which is generally perpendicular to the rim axis XI. 
     In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been described and illustrated in its preferred embodiments. However, it must be understood that the invention may be practiced otherwise than as specifically explained and illustrated without departing from the scope or spirit of the attached claims.