Abstract:
A tolerance ring includes a curved strip having first and second ends. Additionally, the tolerance ring includes a plurality of projections formed on the curved strip, and a physical connection between the first and second ends such that the curved strip forms a closed loop.

Description:
FIELD OF THE DISCLOSURE 
       [0001]    This disclosure is concerned with tolerance rings for assembly between an inner component and an outer component, and methods of making and pre-assembling such rings. 
       BACKGROUND 
       [0002]    Typically, a tolerance ring comprises a strip of resilient material, e.g. a metal such as spring steel, which is rolled so that the ends are brought towards one another to form a ring split through its circumference. The split can allow the ring to conform to the shape of the shaft and/or bore during assembly and, in some cases, in service. One or more lines of projections can be formed around the ring, the projections extending radially inwardly and/or outwardly from the ring. The projections can be formations such as corrugations, ridges, waves, dimples or spring fingers. 
         [0003]    In use, the projections can be compressed between the walls of the shaft and bore. Each projection can act like a spring and exerts a radial force against the components, thereby providing an interference fit between them. 
         [0004]    Tolerance rings may facilitate assembly since they can compensate for manufacturing tolerances in the shaft and/or bore. They can also have other benefits, such as compensating for shape and/or dimension changes caused by bore and shaft materials having different thermal expansion properties. In addition, tolerance rings can compensate for angular and radial misalignment of the shaft and bore, and can be used to reduce or control vibration or resonance effects. When an excessive torque is applied to the shaft, a tolerance ring can also allow predictable and repeatable slip to occur. 
         [0005]    However, split ring tolerance rings can be difficult to store, transport and handle loose because they tend to become interlocked and tangled up, as illustrated in  FIG. 1  of the accompanying drawings. This may be a problem for end users, who may have to manually separate the rings. 
       SUMMARY 
       [0006]    In an embodiment, a split ring tolerance ring, at least during transportation and storage, can have its free ends physically connected to form a closed loop. Thus, separation of the free ends during storage and transportation and the consequential risk of interlocking and tangling may be avoided. 
         [0007]    In a first aspect of a tolerance ring can include a curved strip of material having a plurality of projections formed therein, whose free ends are physically connected to form a closed loop. 
         [0008]    Thus, opposite ends of a strip of material can be brought towards one another so that the strip forms a curve or open loop. The ends of the strip can be connected together physically by any suitable means so that the open loop formed by the strip is closed. Accordingly, when a plurality of tolerance rings according to the first aspect are stored or transported together loose in a container the tolerance rings may not become interlocked and tangled. The rings can therefore be retrieved and handled easily by the end user. In particular, the end user need not tug at the tolerance rings to separate them, and so there can be a consequential reduced risk of damage to the rings. 
         [0009]    The free ends of the strip may be separated by a gap or may overlap one another at an end portion. The strip can be made from a resilient material such as carbon steel, stainless steel, inconel, monel, incalloy, phynox, copper-beryllium, or any other suitable material. The projections can be formed in the strip by a press tool and can be formations such as corrugations, ridges, waves, dimples or spring fingers. 
         [0010]    In an embodiment, the physical connection between the free ends of the strip can be adapted to be breakable during radial expansion or contraction of the ring. That is, the physical connection can be temporary or non-permanent. Such radial (and circumferential) expansion or contraction can take place, for example, during pre-assembly of the tolerance ring onto a shaft or into a bore. For example, radial expansion of the ring, and consequential tension across the physical connection between the free ends of the strip, can be caused when the pre-assembly internal diameter of the ring is less than the outer diameter of the shaft. 
         [0011]    This radial expansion or contraction can cause tensile or compressive stresses around the closed loop which in turn can cause the physical connection to be broken so that the free ends of the strip are separated. In this way the tolerance ring can operate in the same way as a known tolerance ring, with the free ends moving towards or away from one another in order to allow for radial expansion and contraction of the ring during assembly and/or during service. 
         [0012]    In an alternate embodiment, the physical connection can be retained in use. To permit radial expansion/contraction during mounting the strip can include an expansion region. The expansion region can act as an expansion joint; it can deform to provide circumferential expansion or contraction corresponding to the radial expansion or contraction of the ring caused during mounting. In this way the expansion region can perform the role that the gap or overlap between the free ends of the strip performs in known tolerance rings: it can enable the circumference of the tolerance ring to grow or shrink so that it can conform to the shape of a shaft or bore. 
         [0013]    The expansion region can extend across the strip, i.e. across the width of the strip. It can extend all the way across the strip, i.e. along the axial extent of the ring. It can be press-formed in the strip, in the same way as the projections. In particular, the expansion region can comprise one or more corrugations. Each corrugation may be a sharp fold, like those of a fan or concertina, or a gentle fold or wave. The corrugation or corrugations can be press-formed in the strip. They can each extend fully across the strip. That is, the corrugations can be folds which are as long as the strip is wide. The expansion region can be located opposite the weld. 
         [0014]    In an embodiment, the physical connection between the free ends of the strip can comprise a weld. The weld can be a tack weld, e.g. a spot weld, designed to be breakable during radial expansion or contraction of the ring. In such embodiments the weld may not extend all the way across the strip, but may instead be small in relation to the width of the strip. The weld can connect one or more overlapping regions of the strip. Each overlapping region can be unformed (i.e. free of projections). The overlapping regions can include one or more finger projections from one end of the strip which are arranged to overlie the other end of the strip when it is curled into a pre-use configuration. 
         [0015]    Alternatively, the weld can be a weld bead. The weld bead can extend across the width of the strip; that is, the weld bead can be as long as the strip is wide. Such a weld bead can be retained in use, so that the free ends of the strip remain physically connected to one another when the tolerance ring is assembled between a shaft and a bore. 
         [0016]    In another aspect, a method of manufacturing a tolerance ring includes: forming a plurality of projections in a strip of material, bending the strip into a curve, and physically connecting the free ends of the strip to form a closed loop. 
         [0017]    In an embodiment, forming the projections can be carried out using any suitable forming method. For example, the projections can be press-formed or roll-formed. The projections can be formed, for example, by indenting the strip to form corrugations, ridges, waves or dimples, or by piercing the strip to form spring fingers. 
         [0018]    The projections can each extend from the strip in the same direction. Thus, in use the projections can extend from the strip in order to frictionally engage a surface of one of an inner component and an outer component. The other of the inner and outer component can thus be engaged by an unformed part of the strip. For example, in one embodiment the projections can engage the external surface of a shaft and the unformed region can engage the inwardly facing surface of a bore (e.g. cavity in a housing). Alternatively, the projections can extend outwardly from the strip in order to frictionally engage the inwardly facing surface of a bore and the unformed region can contact the shaft. 
         [0019]    Bending the strip into a curve can be achieved using any suitable method. For example, the strip can be rolled into a curve. The radial expansion or contraction of the ring comprises radial expansion or contraction of the unformed surface of the ring. That is, a change in radius of an arc or loop formed by the unformed surface of the ring. 
         [0020]    Physically connecting the free ends of the strip can comprise forming a physical connection which is arranged to be breakable during radial expansion or contraction of the ring. The step of press-forming the strip can include forming an expansion region in the strip, the expansion region being arranged to permit radial expansion or contraction of the ring. In such embodiments the physical connection can be retained during use of the tolerance ring. That is, the physical connection can be arranged to be permanent. 
         [0021]    The step of physically connecting the free ends of the strip can comprise welding the free ends to one another. The weld can be a tack weld designed to be temporary and broken when the ring is pre-assembled to a bore or shaft. Alternatively, the weld can be a weld bead and can extend across the strip, e.g. all the way across the strip. 
         [0022]    In yet another aspect, a method of pre-assembling a tolerance ring to a shaft or bore can include the step of either mounting the tolerance ring on the shaft so that the tolerance ring radially expands or mounting the tolerance ring in the bore so that the tolerance ring radially contracts. The tolerance ring can include a curved strip of material having a plurality of projections press-formed therein, whose free ends are physically connected to form a closed loop. 
         [0023]    The tolerance ring can be adapted to be assembled between a shaft and a bore. Initially, though, the ring can be mounted on the shaft or in the bore to form a pre-assembly. The remaining component can be then assembled to the pre-assembly to form the final assembly. When the ring is pre-assembled to the shaft, the outer diameter of the shaft can be greater than the internal diameter of the ring (e.g. the diameter of the unformed surface), so that the ring radially expands during pre-assembly. Similarly, when the ring is pre-assembled to the bore, the internal diameter of the bore can be smaller than the external diameter of the ring (e.g. the diameter of the unformed surface), so that the ring radially contracts during pre-assembly. 
         [0024]    The ring can be pre-assembled to the shaft so that the projections extend radially outwardly from it, i.e. so that the unformed surface is in contact with the shaft. Alternatively, the ring can be pre-assembled to the bore so that the projections extend radially inwardly from it, i.e. so that the unformed surface is in contact with the bore. 
         [0025]    Radial expansion or contraction of the ring can cause breakage of the physical connection between the free ends of the strip. The ring can have an expansion region which permits the radial expansion or contraction of the ring. In such embodiments the physical connection can be retained in use. That is, the physical connection can be arranged to permanently connect the free ends of the strip together. 
         [0026]    Preferred or optional features described in relation to the various aspects of the invention may be applied, either singly or in combination, to any of the aspects. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0027]    By way of example, embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings, in which: 
           [0028]      FIG. 1  shows a plurality of interlinked conventional tolerance rings; 
           [0029]      FIG. 2  shows a tolerance ring according to a first embodiment of the present invention; 
           [0030]      FIG. 3  shows a tolerance ring according to a second embodiment of the present invention; and 
           [0031]      FIGS. 4A ,  4 B and  4 C show schematically three weld configurations for use with the invention. 
       
    
    
     DETAILED DESCRIPTION  
       [0032]    The tolerance rings  10  illustrated in  FIGS. 2 and 3  can each be formed from a rectangular strip, or band,  12  rolled into an open ring shape or loop. The ends of the strip  12  may not meet one another, but can be separated by a gap  14  which splits the ring  10  across its circumference, i.e. across the width of the strip  12 . In other embodiments the ends of the strip  12  can overlap so that, when unconnected, they are able to slide relative to one another in response to changes in diameter of the ring  10 . Each strip  12  can be made from a resilient material such as spring steel, and can have a line of projections  16  press-formed along its length. Thus, the strip  12  can have an unformed surface  22  and a formed surface  24 . 
         [0033]    The projections  16  can extend radially outwardly from the ring  10  so that they contact the walls of the bore when the ring  10  is assembled in the annular space between a shaft and bore (not shown). In use, the projections  16  can be compressed between the walls of the shaft and bore. Each projection  16  can act like a spring and exerts a radial force against the components, thereby providing an interference fit between them. 
         [0034]    Although the illustrated embodiments show a tolerance ring  10  in which the projections  16  extend radially outwardly so that the unformed surface  18  contacts the shaft and the formed surface  20  contacts the bore, in an alternate embodiment the projections can extend radially inwardly. 
         [0035]    In the embodiment of  FIG. 2  the gap  14  can be bridged by a breakable weld  22 , such as a tack weld or spot weld. In practice this may be achieved by providing an overlap portion (see  FIGS. 4A-4C  for examples). The overlap portion can be one or more tabs of unformed material attached to (or integrally formed with) one end of the strip  12 . It can be arranged to overlap with and be weldable to an unformed region at the other end of the strip  12  when the strip is curled ready for use. In embodiments in which the free ends of the strip  12  overlap one another the weld can be typically positioned across the outermost free end. One or both of the free ends may have a plain (i.e. unformed) region with no projections in order to enable face-to-face mating of the free ends. 
         [0036]    The ring  10  shown in  FIG. 2  can be designed to be either larger in external diameter than the internal diameter of the bore into which it is to be assembled or smaller in internal diameter than the external diameter of the shaft onto which it is to be assembled. Thus, when the ring  10  is pre-assembled around a shaft or within a bore the ring  10  can be deformed either by radial expansion or radial contraction. This deformation can cause either tensile or compressive strains to be applied to the weld  22  so that it breaks. Accordingly, after assembly the ring  10  can perform in exactly the same way as a conventional tolerance ring since the break or split between the free ends of the strip  12  is reinstated. This break or split allows the ring  10  to conform to the shape of the shaft and/or bore to which it is assembled. The portions of the weld  22  remaining on the free ends of the strip  12  after breakage of the weld  22  can remain attached thereto after assembly of the ring  10  between a shaft and bore. 
         [0037]    In the embodiment of  FIG. 3 , on the other hand, the gap  14  can be permanently bridged by a weld bead  24 . In order to enable the ring  10  to conform to the shape of the shaft and/or bore to which it is assembled, the ring  10  can have an expansion joint  26  opposite the gap  14 . The expansion joint  26  can comprise a series of corrugations  28  which deform in order to provide a certain degree of circumferential expansion and contraction. In this embodiment, the expansion joint  26  can include a plurality of folds, but an expansion joint having only one fold may also be used. Thus, the ring  10  can be able to conform to the shape of the shaft and bore between which it is assembled, even though the gap  14  is welded closed. For example, if the pre-assembly outer diameter of the tolerance ring  10  is greater than the internal diameter of the bore, the corrugations  28  will fold towards one another so the outer diameter (and circumference) of the ring  10  can be correspondingly reduced. 
         [0038]      FIGS. 4A to 4C  show three examples of weld arrangements. 
         [0039]    In  FIG. 4A  the curved strip of material  40  (shown flat in the drawings for convenience) can have a plurality of projections  42  can be formed therein. The projections  42  are formed in two circumferential rows separated by an unformed region  43 . When the strip is in a pre-use position, i.e. after curling but before mounting on a component, the ends of the strip  40  can be separated for most of their axial length by an axial gap  44 . However, one end of the strip  40  can have a central circumferential tab  46  which acts as an overlap portion. The tab  46  can be cut out of an unformed end of the strip. The tab  46  can be unformed and aligned with the unformed region  43  between the projections so that it overlies part of the other end when the strip is in the pre-use position. A weld  48  can attach the overlapping parts to each other to provide a physical connection between the ends of the strip  40  to form an unbroken ring. 
         [0040]      FIG. 4B  shows a similar strip  40  where the whole axial extent of an unformed end  50  of the strip overlaps with the other end. In this embodiment two axially separated spot welds  48  can provide the physical connection. An advantage of this arrangement is that it is only necessary to position accurately the welding equipment and strip in one dimension to achieve a useful weld. 
         [0041]      FIG. 4C  shows another similar strip  40  where there are three tabs  56 ,  58 ,  60  extending from one end of the strip  40 . A weld  48  can be provided where each tab  56 ,  58 ,  60  overlaps with the other end of the strip so that each tab can perform a similar function to the tab  46  discussed with reference to  FIG. 4A . Two of the tabs  56 ,  58  can be provided at the axial edges of the strip, where they can be aligned with unformed regions  52 ,  54  which can run along the top and bottom edges of the strip  40 . The third tab  60  can be located centrally to be aligned with the unformed region  43  between the sets of projections. An advantage of this arrangement is that the welds can be provided on either side of the final projections at the end of the strip.