Abstract:
A method of manufacturing a steering column assembly having a first jacket and a second jacket with a bushing between the first and second jackets. The method utilizes a manufacturing machine having a loadable member, a fixed member, and a thermal fixture. The method comprises the steps of: assembling the first jacket to the second jacket with the bushing located radially between the first and second jackets to interlock the first and second jackets and prevent axial movement between the first and second jackets; connecting the first jacket to the loadable member of the manufacturing machine; connecting the second jacket to a fixed member of the manufacturing machine; loading the loadable member to apply an axial force to the first jacket; heating the thermal fixture of the manufacturing machine; and melting the bushing until the first jacket moves axially relative to the second jacket.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a machine for manufacturing a steering column and more particularly to a method of manufacturing a steering column assembly. 
       BACKGROUND ART 
       [0002]    Current production telescoping steering columns traditionally use an injection molded plastic telescoping bushing, i.e. telebushing that once assembled between the column jackets is over-molded with a plastic injection process. Secondary processes such as “wiping” the jackets may also be performed to provide consistent telescoping loads. This over-mold process functions to take-up tolerance variations between the jackets, thus eliminating lash between the components. Unfortunately, the over-mold injection machines for this process require significant capital investment. Moreover, the process of “wiping” jackets to achieve consistent telescoping loads is expensive and labor intensive. 
         [0003]    Accordingly, it would be desirable to develop a manufacturing machine and a method of manufacturing a steering column that overcame the deficiencies of the prior art while taking-up the necessary tolerance variations. 
       SUMMARY OF THE INVENTION 
       [0004]    Accordingly, it would be desirable to develop a manufacturing machine and a The present invention provides a method of manufacturing a steering column assembly having a first jacket and a second jacket with a bushing between the first and second jackets. The method utilizes a manufacturing machine having a loadable member, a fixed member, and a thermal fixture. The method comprises the steps of: assembling the first jacket to the second jacket with the bushing located radially between the first and second jackets to interlock the first and second jackets and prevent axial movement between the first and second jackets; loadable member to apply an axial force to the first jacket; heating the thermal fixture of the manufacturing machine; and melting the bushing until the first jacket moves axially relative to the second jacket. 
         [0005]    The present invention also provides the steering column manufacturing machine for manufacturing the steering column having the first jacket in telescopic relation to the second jacket with the bushing located between the first and second jackets. The manufacturing machine comprises a loadable first member for releasable connection to the first jacket and a second member for releasable connection to the second jacket and axially opposing the first member. A thermal fixture is constructed and arranged to be heated for heating of the bushing through one of the first and second jackets. 
         [0006]    Accordingly, the present invention includes a method and an associated manufacturing machine for manufacturing a steering column, that melts a bushing to thermally size the bushing and thus provide a consistent operation load between the inner and outer jackets when moving between extended and retracted positions while avoiding the deficiencies of the prior art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    These and other objects, features and advantages of this invention will be apparent from the following detailed description, appended claims, and accompanying drawings in which: 
           [0008]      FIG. 1  is a cross section of a steering column manufacturing machine embodying the present invention and in a preloaded state; 
           [0009]      FIG. 2  is a cross section of the steering column manufacturing machine in an unloaded state; 
           [0010]      FIG. 3  is a cross section of the steering column manufacturing machine taken along line  3 - 3  of  FIG. 1 ; 
           [0011]      FIG. 4  is an enlarged cross section of the steering column manufacturing machine taken from circle  4  of  FIG. 1 ; 
           [0012]      FIG. 5  is an enlarged cross section of the steering column manufacturing machine taken from circle  5  of  FIG. 3 ; and 
           [0013]      FIG. 6  is an enlarged cross section of the steering column manufacturing machine taken from circle  6  of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    Referring to the Figures, wherein like numerals indicate like or corresponding parts, a steering column assembly is generally shown at  20  in  FIGS. 1 and 4 . The steering column assembly  20  has an inner or first jacket  22 , an outer or second jacket  24  and a bushing  26  located between the inner and outer jackets  22 ,  24 . Preferably, the inner and outer jackets  22 ,  24  are tubular in shape with the inner jacket  22  telescopingly disposed within the outer jacket  24  for movement along a longitudinal axis or centerline  28 . A cavity is defined between the inner and outer jackets  22 ,  24 . 
         [0015]    As also shown in  FIG. 3 , the bushing  26  is preferably a telebushing that is radially disposed about the inner jacket  22  within the cavity between the inner and outer jackets  22 ,  24 . The bushing  26  provides a substantially consistent load during telescopic movement of the jackets  22 ,  24  between an extended position and a retracted position. The bushing  26  is preferably tubular and split longitudinally to form a gap  36  circumferentially between two distal ends  38 ,  40  of the bushing  26 . The gap  36  assists in the snug fit of the bushing radially between the jackets  22 ,  24 . 
         [0016]    The bushing  26  includes at least one tab  46  engaging the inner jacket  22  to interconnect the bushing  26  to the inner jacket  22  to prevent relative axial and rotational movement therebetween. The inner jacket  22  preferably includes a hole  48  for accepting the tab  46  of the bushing  26 . The snap fit of the tab  46  in the hole  48  axially and circumferentially aligns the bushing  26  with the jackets  22 ,  24 . 
         [0017]    As also shown in  FIG. 5 , the bushing  26  also includes at least one radially projecting pad  42 , preferably a plurality of pads  42 , engaging the outer jacket  24  to frictionally interconnect the bushing  26  to the outer jacket  24 . In the embodiment illustrated, diametrically opposed to the gap  36  are two axially spaced pads  42  of the bushing  26  that project radially outward and press directly against a cylindrical inner surface  44  of the outer jacket  24 . Additional pads  42  are circumferentially spaced about the jackets  22 , 24  as necessary. It should be appreciated that any number of pads  42  may be axially and/or circumferentially spaced about the jackets  22 ,  24 . Welds in the outer jacket  24 , for attachment of brackets, etc., often tend to locally deform the outer jacket  24  of the weld sites. It is therefore desirable that the pads  42  be spaced from the weld sites so as to not affect the stroke performance of the inner jacket. 
         [0018]    The bushing  26  initially interlocks the inner and outer jackets  22 , 24  and prevents axial movement between the inner and outer jackets  22 , 24 . As discussed in greater detail below, the pads  42  are meltable for thermally sizing the bushing  26  to allow relative movement between the inner and outer jackets  22 , 24  and to uniformly load the inner and outer jackets  22 , 24  during telescoping movement of the steering column assembly  20 . In the preferred embodiment, the bushing  26  includes an inner surface and an opposing outer surface with the tab  46  projecting inwardly from the inner surface and the pad  42  projecting outwardly from the outer surface. 
         [0019]    A steering column manufacturing machine  50  is provided for manufacturing the steering column assembly  20  having the jackets  22 , 24 . The machine  50  has a loadable first member or cylinder  52  for releasable connection to the first or inner jacket  22 . The machine  50  also has a rigidly fixed second member  54  for releasable connection to the second or outer jacket  24 . The second member  54  is axially opposed to the first member  52 . A bracket  56  of the machine  50  is contoured in a concave fashion to accept and secure a cylindrical shape of the outer jacket  24 . 
         [0020]    The first member  52  may be an air or hydraulic cylinder or may be a ball screw apparatus with a servo. The first member  52  includes a load cell  58  for setting and controlling the first member  52  to the desired operation load. Because operation of the machine  50  is generally compressive (i.e. the first member  52  moves toward the second member  54 ) attachment of distal ends of the jackets  22 ,  24  to the respective first and second members  52 ,  54  does not require clamping engagement or separate fasteners. Instead, each member  52 ,  54  is contoured and/or has a recess sized to snugly fit the ends of the respective jackets  22 ,  24 . 
         [0021]    A thermal fixture  60  of the machine  50  is constructed and arranged to be heated for heating the bushing  26  through one of the first and second jackets  22 , 24 . The bracket  56  orientates the steering column assembly  20  diametrically opposed to the thermal fixture  60 . The thermal fixture  60  has a housing  62  for direct contact with one of the first and second jackets  22 , 24  and at least one, preferably a plurality, of electric heating elements  64  contained inside the housing  62 . Preferably and integral to the housing  62  are two inverted platforms  66 . The platforms  66  are spaced axially apart from one another by a distance that is substantially equal to the spacing of the pads  42  to be heated. Each platform  66  therefore heats a respective pad  42 . A controller  68  of the machine  50  preloads the first member  52  and moves the fixture  60  and the platforms  66  between a pre-staged state and a heating state. In the heating state, the platforms  66  are directly against an outer surface of one of the jackets  22 , 24 , preferably the outer jacket  24 , when heating the bushing  26  and radially away from the jackets  22 , 24  when not heating. Preferably, the first member  52  is preloaded when the thermal fixture  60  is in the heating state. 
         [0022]    As also shown in  FIG. 6 , the steering column manufacturing machine  50  manufactures the steering column assembly  20  by thermally sizing the bushing  26  thus providing a consistent operation load or force between the inner and outer jackets  22 ,  24  when moving between the extended and retracted positions. During fabrication of the steering column assembly  20  and operation of the machine  50 , the first jacket  22  is assembled to the second jacket  24  with the bushing  26  located radially between the jackets  22 , 24  to initially interlock the jackets  22 , 24  and prevent axial movement between the jackets  22 , 24 . In particular, the bushing  26  is slid over the inner jacket  22  until the tab  46  snap fits into the hole  48  of the inner jacket  22  assuring that the bushing  26  is properly aligned. An axial frictional threshold force is then applied to the jackets  22 ,  24  forcing the inner jacket  22  into the outer jacket  24  thereby biasing the interference pads  42  tightly against the inner surface  44  of the outer jacket  24 . This frictional threshold force is greater than a designed or operational force of the steering column assembly  20  during normal operation. The operational force is generally that axial force required to telescope the steering column assembly  20  between the retracted position and the extended position. 
         [0023]    The steering column assembly  20  is then placed in the machine  50  with a distal end of the first or inner jacket  22  preferably releasably connected to the loadable member  52  and a distal end of the second or outer jacket  24  releasably connected to the fixed member  54  of the machine  50 . The loadable member  52  is then axially loaded with the operational force and in a direction toward the fixed member  54  by the controller  68  to apply an axial force to the first jacket. Once the steering assembly column  20  is properly seated to the bracket  56  and members  52 ,  54 , the controller  68  moves the thermal fixture  60  from the pre-staged state  72 , where the elements  66  are spaced radially outward from the outer jacket  24 , and to the heating state  70  where the elements  66  are, preferably, in direct contact with the outer surface of the outer jacket  24 . 
         [0024]    When in the heating state, the controller  68  energizes the heating elements  64  (if not continuously energized) to heat the thermal fixture  60 . In the heating state, thermal conduction occurs to heat through the jacket  24  and melt the bushing  26  until the first jacket  22  moves axially relative to the second jacket  24 . As mentioned above, the axial load is equal to the normal operational force. Hence, when the axial movement of the jackets  22 , 24  occurs, the bushing  26  has melted to the preferred size to ensure proper operational movement of the jackets  22 , 24 . Preferably, the jackets  22 ,  24  are formed of a metallic material capable of transmitting heat and the bushing  26  is formed of a self-lubricating plastic material with a melting point generally compatible with the heating fixture  60 . Even more preferably, the melting of the bushing  26  further includes the step of migrating the melted bushing  26  about the jackets  22 , 24  to thermally size the bushing  26  such that the jackets  22 , 24  are uniformly loaded during telescoping movement of the steering column assembly  20 . The step of melting the bushing  26  is further defined as melting the pads  42  directly through the outer jacket  24 . In the most preferred embodiment, the thermal fixture  60  is aligned with the pads  42  to be heated for adequately melting these pads  42  of the bushing  26 . 
         [0025]    When a portion of the pads  42  begin to melt, such as shown in  FIG. 6 , the jackets  22 , 24  will begin to move axially which will in turn cause the melted bushing  26  to migrate or wipe against the outer jacket  24 . During this axial movement, the biasing threshold force is generally or partially relieved. As this biasing force is reduced generally to or slightly below the loaded force of the loadable member  52 , the steering column assembly  20  will begin to retract toward the retraced position. Upon this axial movement, the controller  68  will cause the heating fixture  60  to move radially outward and back into the pre-staged state spaced from the jackets  22 , 24 . The bushing  26  is thus formed between the jackets  22 ,  24  with a consistent and reliable operational force during normal telescoping movement of the steering column assembly  20 . The inner jacket  22  may be further stroked to a cold location on the outer jacket  24  to quench the melted pads  42  and arrest any thermal deformation. 
         [0026]    Preferably, the jacket of the assembly  20  that is stationary in the vehicle during normal use is the jacket in direct contact with the melted pads  42  for consistent results. As described above, it is the outer jacket  24  that is stationary. However, one skilled in the art would now realize that if the inner jacket  22  were to be stationary, the pads  42  of the bushing  26  could project radially inward and directly contact the inner jacket  22 . In this case, the heating fixture  60  may be located radially inward of the inner jacket  22  for melting of the pads  42 . 
         [0027]    While the forms of the invention herein disclosed constitute presently preferred embodiments, many others are possible. It is not intended herein to mention all the possible equivalent forms or ramification of the invention. It is understood that terms used herein are merely descriptive, rather than limiting, and that various changes may be made without departing from the spirit or scope of the invention.