Abstract:
A bearing expansion lock useful in locking linear axial movement of a push-pull rod driven by a potential energy source, where the push-pull rod is housed in a hollow shaft, is disclosed. A hollow elongated housing is provided to be mounted along an axial dimension of the hollow shaft. A shaft subassembly is received within the housing and adapted to be interposed between an outboard end of the push-pull rod and the potential energy source. The shaft subassembly is reconfigurable between a first position in which the shaft subassembly is braced against slidable movement within the housing along the hollow shaft and a second position in which the shaft subassembly is slidable within the housing along the central shaft. Configuration of the shaft subassembly in the first position restricts movement of the shaft subassembly along the housing, thereby restricting movement of the push-pull rod along the hollow shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 61/366,748, filed on Jul. 22, 2010. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of Invention 
         [0004]    This invention pertains to tire building equipment. More particularly, this invention pertains to a lock for locking a slidable member within a sleeve, the lock being useful, for example, in conjunction with an expandable and collapsible tire building drum for the manufacture of tires. 
         [0005]    2. Description of the Related Art 
         [0006]    Commonly, the process of manufacturing a tire, such as a motor vehicle tire, includes fabrication of a cylindrical carcass as a precursor to the tire. A tire carcass is formed by laying down components of the tire on the outer circumference of a rotatable, expandable and collapsible drum. Such drums must be adjustable with respect to their diameter, hence their outer circumference, first, to establish a desired outer circumference of the drum, and second, to collapse the drum for removing a completed carcass from the drum. 
         [0007]    Adjustablility of the diameter of tire building drums commonly involves a plurality of segments which are moveable between radially collapsed positions internally of the drum and radially expanded positions in which the segments collectively define the outer circumference of the drum. U.S. Pat. No. 6,390,166 (“the &#39;166 patent”), which patent is incorporated herein in its entirety by reference, discloses a tire building drum of this type. The device of the &#39;166 patent includes generally a plurality of segments collectively defining the outer circumferential surface of a generally cylindrical drum. The segments are mounted by way of a system of linkages about a central main shaft which allows the segments to be selectively repositionable between expanded positions radially of the rotational axis of the drum and collapsed positions radially of the drum in which a portion of the segments are brought into overlying relationship with other of the segments to collapse the diameter of the drum. Positioning the segments in the expanded positions provides a relatively continuous circumferential outer surface of the drum, thereby permitting layup of various components of a tire carcass thereon for forming of the tire carcass. Positioning the segments in the collapsed positions collapses the diameter (and circumference) of the drum to permit the removal of a formed tire carcass from the drum. 
         [0008]    In the device of the &#39;166 patent, control of the selective repositioning of the segments between the expanded and collapsed positions is provided for by means of a push-pull rod which is received within a hollow outboard end of the main shaft and mounted therein for axial sliding movement relative to the main shaft. Reciprocatory movement of this push-pull rod activates other mechanism(s) internally of the drum to effect radial expansion and contraction of the segments of the drum. Accordingly, an outboard end of the push-pull rod is bored and tapped to be engaged by an actuating mechanism associated with a tire making machine of the type known in the art. This actuating mechanism functions to selectively move the push-pull rod axially within the main shaft to thereby effect radial adjustment of the segments and selection of the diameter (circumference) of the drum. 
         [0009]    Once the tire building drum is expanded to its desired diameter, the moving parts of the tire building drum must be rigidified so that the segments will maintain their expanded state under the forces to which the tire building drum is subjected in the course of forming of the carcass. In several configurations of tire building drums and tire making machines of the type known in the art, the actuating mechanism for engaging and moving the push-pull rod of the tire building drum includes an external piston/cylinder which is powered by pressurized fluid to actuate the push-pull rod. There are large numbers of tire building drums in existence, and new tire building drums are being produced and introduced into the marketplace, wherein the tire building drum has no internal mechanism, other than the continued application of a force upon the push-pull rod by means of the pressurized fluid, for locking the segments in their most outwardly radial positions after the segments have been so positioned. In these tire building drums, failure to maintain the “push” pressure against the push-pull rod results in radial collapse of the segments thereby destroying the usefulness of the tire building drum. Moreover, in these latter tire building drums, should the value of the pressure applied to the push-pull rod diminish below that value which is required to maintain the segments in their fully expanded positions, for any reason, during the laying up of a tire component on the outer circumference of the tire building drum, the segments can collapse and destroy the component being formed. 
         [0010]    Furthermore, in certain prior art tire building drums including the device of the &#39;166 patent, the mechanical nature of the positioning, sizing, and assembly of a multiplicity of interacting components of the tire building drum results in a relatively small, but important, degree of lost motion when the direction of movement of the push-pull rod is reversed. As much as 0.7 inch of lost motion is not uncommon in the prior art tire building drums. Unless accommodated for, this lost motion can result in deleterious gaps between adjacent ones of the segments, hence variation in the circularity of the outer circumference of the tire building drum and a resulting non-circular tire component being formed on the tire building drum. Such non-circular components translate into noncircular tires that are unusable. 
         [0011]    To accommodate this lost motion, it has been the practice to continue the application of pressure against the push-pull rod even after the segments have attained their desired full radially outwardly limit of movement, thereby maintaining the overall mechanical system in a degree of compression so that the segments are forced to remain in their most radially outward positions until a carcass or other tire component has been formed on the tire building drum and the diameter of the tire building drum is to be reduced for removal of the formed component. This action ensures that the outer circumference of the tire building drum remains uniformly circular i.e., without gaps between adjacent segments throughout the formation of a vehicle tire component, such as a torodial tire carcass, thereby ensuring that the resulting carcass is of the desired final uniform internal diameter and of uniform toroidal geometry. 
         [0012]    In the device of the &#39;166 patent and other like tire building drums, most commonly, the expansion force for the tire building drum segments is pressurized air. Maintenance of the expanded state of these tire building drums, i.e., locking of the tire building drum in its expanded state, is by maintaining pressurized air against the moving elements of the tire building drum for the duration of that time within which a carcass or other tire component is being formed on the tire building drum. However, such continued application of force against the push-pull rod introduces the potential for developing destructive forces should one or more of the components of the tire building drum fail while in compression. Thus, such pressurized air “locking” of the drum has been suggested to be a potential safety hazard for operators of the equipment under certain operating circumstances and especially in the event of catastrophic failure of one or more of the mechanical components of the tire building drum. 
       BRIEF SUMMARY OF THE INVENTION 
       [0013]    The present general inventive concept is useful for example in locking axial movement of a push-pull rod driven by a potential energy source suitable for effecting linear axial movement of the push-pull rod, where the push-pull rod is housed in a hollow shaft. According to one embodiment of the present general inventive concept, a bearing expansion lock is provided which includes a hollow elongated housing adapted to be mounted along an axial dimension of the hollow shaft. A shaft subassembly is received within the housing and is adapted to be interposed between an outboard end of the push-pull rod and the potential energy source. The shaft subassembly is generally reconfigurable between a first position in which the shaft subassembly is braced against slidable movement within the housing along the hollow shaft and a second position in which the shaft subassembly is slidable within the housing along the central shaft. Configuration of the shaft subassembly in the first position restricts movement of the shaft subassembly along the housing, thereby restricting movement of the push-pull rod along the hollow shaft. 
         [0014]    In one embodiment of the general inventive concept, the shaft subassembly includes a shaft having an inboard end and an outboard end. The shaft inboard end is adapted to be secured to the push-pull rod. A circumferential flange extends from the shaft between the shaft inboard and outboard ends. One embodiment of the general inventive concept further includes a ball cage defining a plurality of through cavities. Each through cavity has a ball bearing at least partially embedded therein. The ball cage is slidably disposed along the shaft between the first position, in which the flange engages at least one of the ball bearings to bias the ball bearing toward the housing, and the second position, in which the flange is disengaged from the ball bearings. In one embodiment of the general inventive concept, the plurality of through cavities are disposed in an annular array about the ball cage surrounding the shaft. 
         [0015]    In one embodiment of the general inventive concept, the shaft subassembly further includes an annular bushing surrounding the shaft with a first end extending between the shaft and the ball cage and a second end extending along the shaft opposite the ball cage from the flange. In one embodiment, a resilient assembly is disposed between the ball cage and the bushing second end. The resilient assembly is compressible between the ball cage and the bushing second end to bias the ball cage toward the flange to maintain engagement of the flange with the ball bearings in the first position. In one embodiment, the resilient assembly includes a resilient annular ring disposed surrounding the shaft between the ball cage and the bushing second end. In another embodiment, the resilient assembly includes a plurality of springs disposed surrounding the shaft between the ball cage and the bushing second end. 
         [0016]    In one embodiment of the general inventive concept, separation of the ball cage from the bushing second end along the shaft is restricted. For example, in one embodiment, a collar is provided surrounding the resilient assembly to capture the resilient assembly between the ball cage and the bushing second end. In one embodiment, the collar is defined by a split collar surrounding the resilient assembly and limiting separation of the ball cage from the bushing second end along the shaft. 
         [0017]    In one embodiment of the general inventive concept, the shaft subassembly further includes a cap having an inboard end secured to and surrounding the bushing second end and the shaft outboard end. An outboard end of the cap defines a connector adapted to secure the cap to the source of potential energy suitable for effecting linear axial movement of the push-pull rod. In one embodiment, the connector is defined by a neck portion integrally formed with the cap outboard end and a circumferential flange defined at a terminus of the cap outboard end. The cap is sized to allow intimate slidable engagement with an interior surface of the housing. 
         [0018]    The shaft subassembly is adapted to be slidably received within the housing. In one embodiment, the housing interior surface defines a cylindrical shape, and the ball cage and collar are each sized to allow intimate slidable engagement with the interior surface of the housing. 
         [0019]    In certain embodiments, the present general inventive concept is included in a rotatable drum useful in the manufacture of a vehicle tire or component thereof, wherein the drum includes a housing and a plurality of outer circumferential surface-defining segments which are radially positionable relative to the rotational axis of the drum by means including linear axial movement of a push-pull rod, housed within a central shaft, by a potential energy source suitable for effecting linear axial movement of the push-pull rod. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0020]    The above-mentioned features of the invention will become more clearly understood from the following detailed description of the invention read together with the drawings in which: 
           [0021]      FIG. 1  is a perspective view of a tire building drum including one embodiment of a bearing expansion lock constructed in accordance with several features of the present invention; 
           [0022]      FIG. 2  is a cross-sectional side view of the tire building drum and bearing expansion lock of  FIG. 1 ; 
           [0023]      FIG. 3  is a partial cross-sectional side view of the tire building drum of  FIG. 2 , showing a close up view of the bearing expansion lock; 
           [0024]      FIG. 4  is an exploded perspective view of the bearing expansion lock of  FIG. 2 ; 
           [0025]      FIG. 5  is an exploded cross-sectional side view of the bearing expansion lock of  FIG. 2 ; 
           [0026]      FIG. 6  is a cross-sectional side view of the bearing expansion lock of  FIG. 2 , showing the bearing expansion lock in the first position; 
           [0027]      FIG. 7  is a cross-sectional side view of the bearing expansion lock of  FIG. 2 , showing the bearing expansion lock in the second position; and 
           [0028]      FIG. 8  is an exploded perspective view of another embodiment of a bearing expansion lock constructed in accordance with several features of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    A bearing expansion lock  10  is disclosed herein and in the various figures. The bearing expansion lock  10  of the present invention provides an improvement in a prior art tire building drum  12  which is useful in the manufacture of vehicle tires. 
         [0030]    With initial reference to  FIGS. 1 and 2 , a tire building drum  12  is depicted. The tire building drum  12  is of the push-pull type wherein the drum is mounted for rotation on a central shaft  14 . The shaft of the depicted drum is hollow and houses therein a push-pull rod  16  that is mechanically connected to a plurality of outer shell segments  18  (typical) which collectively define the outer circumferential working surface of the tire building drum  12 . As discussed above, each segment is mounted for radial movement inwardly and outwardly of the tire building drum  12  upon actuation through linear axial movement of the push-pull rod  16 . Actuation of the push-pull rod commonly is effected by means of a piston/cylinder device  20  that is powered from a source of pressurized fluid  22 , most commonly pressurized air. When the push-pull rod  16  is pushed axially inwardly of the tire building drum  12  along the central shaft  14 , the segments  18  simultaneously move radially outwardly of the tire building drum  12  to collectively define the outer circumferential surface  24  of the tire building drum  12 . When the push-pull rod  16  is pulled in a direction outwardly of the tire building drum  12  along the central shaft  14 , the segments  18  are moved radially inwardly of the tire building drum  12  to reduce its diameter, such as for removal of a formed toroidal tire carcass from the outer circumferential surface  24  of the tire building drum  12 . U.S. Pat. No. 6,390,166 provides further structural and operational information relating to this type of tire building drum  12  and is incorporated herein in its entirety by reference. 
         [0031]    Referring to  FIG. 2 , in one embodiment of the present invention, the end  26  of the tire building drum  12  from which the push-pull rod  16  is accessible for operation of the push-pull rod  16  is provided with a bearing expansion lock  10  of the present invention. In the depicted embodiment, reciprocatory movement of the push-pull rod  16  is effected by means of a double-acting piston/cylinder  20  within which a piston  32  is reciprocatably mounted, and which is powered by the source  22  of pressurized fluid, commonly air, that is connected in fluid communication with the piston/cylinder as by conduits  34  and  36 . Referring to  FIGS. 2 and 3 , in accordance with one aspect of the present invention, the bearing expansion lock  10  of the present invention is interposed between the outboard end  38  of the piston  32  and the outboard end  40  of the push-pull rod  16 . This bearing expansion lock, or lock  10 , generally comprises a shaft subassembly  30  which is slidably disposed within a cylindrical housing  38  mounted in the end  26  of the central shaft  14  of the tire building drum  12  (or the tire building drum housing, as appropriate) and which is anchored in the outboard end  40  of the push-pull rod  16 . 
         [0032]    Referring to  FIGS. 3-7 , the shaft subassembly  30  includes a shaft  42  having an externally threaded inboard end  44  adapted to be threadably received within a central internally threaded blind bore  46  provided in the outboard end  40  of the push-pull rod  16 , and an externally threaded outboard end  48 . In the illustrated embodiment, the shaft outboard end  48  is provided with at least one depression  50  adapted to receive a tool for threadably assembling the shaft inboard end  44  with the internally threaded blind bore  46  of the push-pull rod  16 . Adjacent the shaft inboard end  44 , the shaft  42  defines an annular circumferential flange  52  which extends substantially perpendicularly of the shaft  42 . An outboard surface of the shaft flange  52  is beveled to define a tapered outer surface  56  thereon. 
         [0033]    Between the shaft flange  52  and the shaft outboard end  48 , there is provided an annular ball cage  58  which encircles the shaft  42  and carries an array of ball bearings  68  partially embedded therein. Referring to  FIGS. 5-6 , the ball cage  58  defines a generally cylindrical wall  64  defining an annular array of through cavities  66 , each of which is sized to partially receive therein a ball bearing  68  (typical). Each through cavity  66  is contoured to permit a corresponding ball bearing  68  to project from both the interior surface  62  and exterior surface  72  of the ball cage  58 , and each through cavity  66  is sized to allow radial inward and outward movement of its corresponding ball bearing  68  toward and away from the shaft  42 . The wall  64  of the ball cage  58  is of a thickness less than the diameter of each ball bearing  68 , such that radially outward movement of a ball bearing  68  to retract the ball bearing  68  from projection from the interior surface  62  of the ball cage  58  results in projection of the ball bearing  68  from the exterior surface  72  of the ball cage  58 . 
         [0034]    The interior surface  62  of the ball cage  58  is sized to permit slidable axial movement of the ball cage  58  along the shaft  42 , and also to permit the shaft  42  to rotate within the ball cage  58 , hence to rotate upon rotation of the push-pull rod  16  relative to the cylindrical housing  38 , as needed. An inboard end  70  of the ball cage interior surface  62 , including the portion of the interior surface  62  along the array of through cavities  66 , is beveled to define a tapered inner surface  74  similar in dimension to the tapered outer surface  56  of the shaft flange  52 . Thus, sliding movement of the ball cage  58  along the shaft  42  toward the shaft flange  52  brings the tapered outer surface  56  of the shaft flange  52  into close conformity with the tapered inner surface  74  of the ball cage  58 , and thus into engagement with those portions of the ball bearings  68  projecting inwardly from the interior surface  62  of the ball cage  58  to bias the ball bearings  68  toward radially outward projection from the exterior surface  72  of the ball cage  58 . Conversely, sliding movement of the ball cage  58  along the shaft  42  away from the shaft flange  52  produces a void space between the ball cage  58  and the shaft flange  52  interior of the ball cage  58  to permit radially inward projection of the ball bearings  68  from the interior surface  62  of the ball cage  58 . 
         [0035]    In the illustrated embodiment, an outboard end  75  of the ball cage  58  terminates at an outwardly extending annular circumferential flange  84 . A bushing  76  is slidably positioned along the shaft  42  outboard of the ball cage  58  and extending inboard between the ball cage outboard end  75  and the shaft  42  to maintain coaxial alignment between the ball cage  58  and the shaft  42  and to enhance the rotational movement of the shaft  42  relative to the surrounding ball cage  58 . An inboard end  78  of the bushing  76  defines a hollow cylindrical portion positioned along the non-tapered outboard portion of the ball cage interior surface  62  between the shaft  42  and the ball cage  58  to stabilize the relative positions of these components. In the illustrated embodiment, a cylindrical spacer  122  is provided between the bushing inboard end  78  and the shaft flange  52  to maintain proper spacing between the bushing  76  and the shaft flange  52  and to provide a bearing for rotational sliding movement between the shaft flange  52  and the bushing  76 . In another embodiment, the bushing inboard end  78  extends sufficiently inboardly along the shaft  42  to maintain proper spacing between the bushing  76  and the shaft flange  52  through abutment of the bushing inboard end  78  with the shaft flange  52 . 
         [0036]    The bushing  76  further defines an outwardly extending annular circumferential flange  80  between the bushing inboard end  78  and an outboard end  82  of the bushing  76 . The bushing flange  80  is positioned in substantially parallel, spaced apart relationship to the ball cage flange  84  to define an annular void  86  therebetween. A collar  96  is positioned surrounding opposite sides of the bushing flange  80  and the ball cage flange  84  to limit separation of the bushing  76  from the ball cage  58  along the axial dimension of the shaft  42 . In the illustrated embodiment, the collar  96  is defined by a two-piece split collar defining a cylindrical body portion  98  surrounding the bushing flange  80 , the ball cage flange  84 , and the void  86 . The collar  96  further defines an outboard, interiorly-extending circumferential wall  99  positioned outboard of the bushing flange  80 , and an inboard, interiorly-extending circumferential wall  100  positioned inboard of the ball cage flange  84 . In certain embodiments, the collar  96  is fixed in relation to at least one of the bushing  76  and the ball cage  58  as by set screws  102  received within appropriate through holes  104  defined in the collar  96 . In other embodiments, the bushing  76  and the ball cage  58  are rotatably slidable within the collar  96  to further facilitate rotational movement of the push-pull rod  16  relative to the cylindrical housing  38 , as needed. 
         [0037]    In several embodiments, a resilient assembly  88  is disposed within the annular void  86  to bias the bushing flange  80  axially from the ball cage flange  84  within the collar  96 . As will be discussed further below, the resilient assembly  88  serves to maintain controlled axial pressure between the bushing  76  and the ball cage  58  during reciprocatory movement of the push-pull rod  16  and lock  10  within the central shaft  14  of the tire building drum  12  to effect engagement of the shaft flange  52  with the ball bearings  68  and the tapered inner surface  74  of the ball cage  58 . In the illustrated embodiment, the resilient assembly  88  is defined by an annular ring  90  formed of a resilient material surrounding the bushing inboard end  78  and interposed between the bushing flange  80  and the ball cage flange  84 . In another embodiment, such as the embodiment of  FIG. 7 , the resilient assembly  88  is defined by a plurality of resiliently compressible springs  92  (typical) interposed between the bushing flange  80  and the ball cage flange  84 . In the illustrated embodiment, each spring  92  is aligned axially along the shaft  42  and is partially received within corresponding cavities  94  defined along each of the bushing flange  80  and the ball cage flange  84  to maintain the springs  92  in a spaced apart relationship about the circumference of the void  86 . Those skilled in the art will recognize other devices and configurations suitable for providing the resilient assembly  88  which may be used without departing from the spirit and scope of the present invention. 
         [0038]    The ball cage  58 , bushing  76 , and collar  96  are, collectively, slidably movable along the shaft  42  between a first position, in which the tapered outer surface  56  of the shaft flange  52  abuts the portions of the ball bearings  68  protruding inwardly from the tapered inner surface  74  of the ball cage  58  to engage and bias the ball bearings  68  toward radially outward projection from the exterior surface  72  of the ball cage  58 , and a second position, in which an outboard end  106  of the bushing  76  abuts a cylindrical bearing  108 , comprising members  110 ,  112 , and  114 , which encircles the shaft  42  adjacent the outboard end  48  of the shaft  42 , thereby providing a sliding seal between the outboard end  106  of the bushing  76  and the shaft  42  and limiting further outboard movement of the bushing  76  along the shaft  42 . In the illustrated embodiment, the shaft  42  defines at least one circumferential lip  116  inboard of the shaft outboard end  48 . The lip  116  is of a diameter slightly larger than an inner diameter of the bearing  108 , such that the lip  116  retains the bearing  108  adjacent the outboard end  48  of the shaft  42 . An internally threaded nut  118  is threadably received onto the externally threaded outboard end  48  of the shaft  42  to thereby capture and retain the various components of the bearing  108 , ball cage  58 , bushing  76 , and collar  96  between the nut  118  and the shaft flange  52 . In the illustrated embodiment, a washer  120  is provided between the nut  118  and the bearing  108  to effect more even load distribution and proper spacing between the nut  118  and the bearing  108 . However, it will be understood that inclusion of the washer  120  is not critical to accomplishment of the present invention. 
         [0039]    Referring to  FIGS. 4-7 , a cap  124  surrounds the shaft outboard end  48 , nut  118 , and bearing  108 , and is secured to the outboard end  106  of the bushing  76 . In the illustrated embodiment, the outboard end  106  of the bushing  76  defines an externally threaded cylindrical shape. The cap  124  includes a generally hollow cylindrical body portion  126  having an open, internally threaded inboard end  130  adapted to be threadably secured to the externally threaded bushing outboard end  106 . An outboad end  128  of the body portion  126  is closed and has formed thereon an integral neck portion  132  which terminates in the form of an enlarged circumferential flange  134 . As may be seen from  FIGS. 2 ,  3 , and  5 , this flange  134  is designed to be received within a side-slotted connector  136  for operative connection of the cap  124  with the outboard end  38  of the reciprocatory rod  28  of the piston/cylinder device  20 , for example, as by means of a threaded nut  138  or like fastener. 
         [0040]    The shaft subassembly  30  is slidably received within the housing  38 . As seen in  FIGS. 2 and 3 , the housing  38  is fitted within the end  26  of the hollow shaft  14  of the drum as by means of external threads  140  on an outboard end  142  of the housing being threadably received within mating internal threads provided within the hollow shaft  14  of the drum. As shown in  FIGS. 6 and 7 , the cap  124 , collar  96 , and ball cage  58  portions of the shaft subassembly  30  are each sized to be of a slightly smaller diameter than an inner diameter of the cylindrical housing  38 . Thus, when the ball cage  58 , bushing  76 , and collar  96  are positioned in the second position ( FIG. 7 ), allowing the ball bearings  68  to be received internally of the ball cage exterior surface  72 , the shaft subassembly  30  is slidably disposed within the hollow cylindrical housing  38 . However, with the shaft subassembly  30  received within the housing  38 , movement of the shaft  42  in relation to the ball cage  58 , bushing  76 , and collar  96  toward the first position ( FIG. 6 ) allows the tapered outer surface  56  of the shaft flange  52  to engage and bias the ball bearings  68  toward an interior surface  142  of the housing  38 , thus allowing the ball bearings  68  to engage the housing interior surface  142  to simultaneously brace the shaft subassembly  30  centrally of the housing  38  and limit slidable movement of the shaft subassembly  30  in relation to the housing  38 . 
         [0041]    It is noted that, with the shaft inboard end  44  fixed in relation to the outboard end  40  of the push-pull rod  16 , longtudinal movement of the shaft subassembly  30  within the housing  38  commences as the drum segments are moved between their radially outward and inward positions for defining and collapsing the outer circumferential working surface of the drum. In the illustrated embodiment, when the rod  28  of the piston/cylinder  20  is moved axially inwardly toward the tire building drum  12  along the central shaft  14 , the rod  28  pushes against the shaft subassembly  30 , which in turn pushes the push-pull rod  16  axially inwardly of the tire building drum  12  to simultaneously move the segments  18  radially outwardly of the tire building drum  12  to collectively define the outer circumferential surface  24  of the tire building drum  12 . As this occurs, the shaft subassembly  30  slides within the housing  38  in the above-discussed second position of the shaft subassembly  30 . Once the segments of the drum have been radially positioned outwardly of the drum in their desired locations to define the outer circumference of the drum, continued extension of the rod  28  and the shaft subassembly  30  along the housing  38  advances the ball cage  58 , bushing  76 , and collar  96  along the shaft  42  toward the first position. As the tapered outer surface  56  of the shaft flange  52  is brought into close conformity with the tapered inner surface  74  of the ball cage  58  to engage and bias the ball bearings  68  toward radially outward projection from the exterior surface  72  of the ball cage  58 , continued extension of the cap  124  and bushing  76  along the shaft  42  pushes the bushing flange  80  toward the ball cage flange  84  to compress the resilient assembly  88  therebetween. Thereafter, axially inward movement of the rod  28  of the piston/cylinder  20  ceases. 
         [0042]    In certain tire building apparatus in which actuation of the push-pull rod is effected by means of a piston/cylinder device  20  that is powered from a source of pressurized fluid  22 , most commonly pressurized air, it is noted that discontinuing axially inward movement of the rod  28  through removal of pressure within the piston/cylinder  20  can result in a small axially outward movement of the rod  28  due, at least in part, to elastic strain in various components of the piston/cylinder device  20 . Accordingly, in certain embodiments in which the resilient assembly  88  is compressed between the bushing flange  80  and the ball cage flange  84  during movement of the shaft subassembly  30  toward the first position, such small axially outward movement of the rod  28  results in partial decompression of the resilient assembly  88 . Thus, as the resilient assembly  88  is partially decompressed, the resilient assembly  88  serves to maintain controlled axial pressure on the ball cage  58  along the shaft  42  toward the first position, thus maintaining pressure of the ball bearings  68  against the housing  38 . 
         [0043]    With the shaft subassembly  30  in the first position, resistance to withdrawal of the shaft subassembly  30  from along the housing  38  is provided by reason of the expansion of the bearings  68  within the housing  38 . Thus, the segment-moving mechanism of the drum is locked against rebound due to, among other things, inadvertent or unintentional loss of the pressure employed to move the segments, and particularly any rebound due to lost motion in the overall mechanism, when the pressure applied to such mechanism to move the segments radially outward of the drum has been released. Withdrawal of the rod  28  outwardly from the tire building drum  12  pulls against the shaft subassembly  30  to first slide the ball cage  58 , bushing  76 , and collar  96  along the shaft  42  toward the first position to unlock the bearings  68  from engagement with the housing  38 , and then to allow the push-pull rod  16  to slide axially outwardly of the tire building drum  12  to move the segments  18  radially inwardly of the tire building drum  12  to collapse the outer circumferential working surface of the drum. 
         [0044]    From the foregoing description, it will be recognized by those skilled in the art that a bearing expansion lock has been provided which is useful in conjunction with a tire building drum in the manufacture of vehicle tires. While the present invention has been illustrated by description of several embodiments and while the illustrative embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant&#39;s general inventive concept.