Abstract:
A telescopic shaft for rapid length adjustment consists of a tube having a plurality of alternating circumferential ridges and grooves on at least a portion of an inner surface and having an oval cross-section with a major diameter D A  and a minor diameter D B ; a shaft disposed within the tube and having matching circumferential ridges and grooves, the shaft also having an oval cross-section with a major diameter D C  and a minor diameter D D ; and the ridges and grooves of the tube interengaging with the grooves and ridges of the shaft when the shaft major diameter D C  is substantially parallel with the tube minor diameter D B .

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates generally to length-adjustable shafts and more particularly to quick-change positive locking telescoping shafts.  
           [0002]    There are innumerable applications in many diverse fields for length-adjustable shafts with positive locking features. One such application is in telescoping adjustable steering columns of motor vehicles, in which it is desirable to be able to quickly change the length of the steering column and to positively lock it in the selected position.  
           [0003]    Many length-adjustable shafts have quick-change capability based on frictional locking mechanisms, similar to collets, in which a tapered ring is threaded on a split tube member to frictionally lock a mating tube or shaft in position within the split tube. These are quite effective, but they provide clamping force which is limited by the operator&#39;s skill in tightening the threaded ring and also by wear and contamination of the clamping surfaces. Also, they do not provide positive locking since the clamping force can be overcome by a large axial load on the shaft.  
           [0004]    Many other current shafts have rack and pawl adjustment locks in which a pawl is pivoted away from a rack on the sliding member of the shaft to allow change of length. When released, the pawl pivots back into engagement with the rack by spring action to lock the shaft in position.  
           [0005]    Currently, still other such shafts are made by threading the inside of a tube and the outside of a mating shaft and then axially cutting away slightly more than half the threads on both members by machining flats on opposing sides of the shaft and arced grooves on opposing sides of the inside of the tube. The shaft can then be inserted in the tube with its remaining threads aligned with the arced grooves of the tube so it slides into the desired position. The shaft is given a quarter turn to lock it in any position relative to the tube. To readjust the length of the shaft/tube couple, it is only necessary to turn either member one-quarter turn and slide it to the new position and re-lock it. These provide quick adjustment and are capable of positive locking, but the presence of burrs at the edges of the machined flats and grooves often prevents turning the tube and shaft to the locked position. Even without burrs, the flats at the edges of the threads on the shaft and tube may butt against each other and prevent turning to the locked position; because they have no normal lead in as would be found in common threads.  
           [0006]    The foregoing illustrates limitations known to exist in present quick-change adjustable length shafts. Thus, it would clearly be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.  
         SUMMARY OF THE INVENTION  
         [0007]    In one aspect of the present invention, this is accomplished by providing a telescopic shaft for rapid length adjustment, comprising a tube having a plurality of substantially circumferential alternating ridges and grooves on at least a portion of an inner surface and having an oval cross-section with a major diameter D A  and a minor diameter D B ; an inner shaft member disposed within said tube and having matching ridges and grooves, the shaft also having an oval cross-section with a major diameter D C  and a minor diameter D D ; and the ridges and grooves of said tube interengaging with the grooves and ridges of said shaft when the shaft major diameter D C  is substantially parallel with the tube minor diameter D B .  
       
    
    
       [0008]    The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIGS. 1 a ,  1   b , and  1   c  are three transverse sectional views of a telescopic shaft of the invention;  
         [0010]    [0010]FIG. 2 is a fragmentary longitudinal partly sectional exploded view of the telescopic shaft; and  
         [0011]    [0011]FIGS. 3 a  and  3   b  are fragmentary perspective views of an alternative embodiment of the inner shaft member and a longitudinal section of the matching outer tube member, respectively. 
     
    
     DETAILED DESCRIPTION  
       [0012]    [0012]FIGS. 1 a ,  1   b , and  1   c  show transverse sectional views of the telescopic shaft  100  of the invention. For best understanding of the features of the invention, it is best to consider FIGS. 1, 2, and  3 , as appropriate, in order to see longitudinal and perspective views when necessary. In its simplest form, the telescopic shaft  100  consists of an outer tube member  10  and an axially slidable inner shaft member  20 , each of which have oval cross-sections and alternating circumferential grooves and ridges (See FIG. 2) or, alternatively, continuous threads on their contacting surfaces. The outer tube member  10  has a major diameter D A  and a minor diameter D B . The inner shaft member  20 , disposed within the outer tube  10 , has matching ridges and grooves and also has an oval cross-section with a major diameter D C  and a minor diameter D D .  
         [0013]    [0013]FIG. 1 a  shows the major diameters D A  of the outer tube member  10  and D C  of the inner shaft member  20  in parallel relationship. In this position the inner shaft member  20  can slide axially within the outer tube member  10 . FIG. 1 b  shows the major diameter D C  of the inner shaft  20  rotated to a position, approaching the minor diameter D B  of the outer tube  10 , in which its grooves  27  and ridges  25  begin to interengage with the ridges  15  and grooves  17  of the tube  10 .  
         [0014]    [0014]FIG. 1 c  shows the outer tube and inner shaft in the fully locked position in which the major diameters are at right angles to each other. Here the ridges  15  of the tube are maximally engaged with the grooves  27  of the shaft, and the ridges  25  of the shaft are maximally engaged with the grooves  15  of the tube. Of course, even though there is a large difference in the diameters of the tube and shaft, the alternating ridges  15  and grooves  17  of the outer tube  10  may tend to engage the alternating grooves  27  and ridges  25  of the inner shaft  20 , merely due to the difficulty of keeping a long shaft centered in a long tube, and make it difficult to slide one relative to the other. To prevent any unwanted engagement, a centering plug  30  may be pivotally mounted on the end of the shaft  20  on a pin or journal  35 . This plug  30  has a slip fit in the outer tube  10  so that it is easily moved, but it just clears the ridges of the tube. The plug  30  keeps the inner shaft  20  properly centered in the outer tube  10 , so there is no unwanted engagement between the ridges and grooves of the members when the shaft is being telescopically adjusted. Of course, when the ridges and grooves of the inner and outer members are prevented from engagement by other means, the centering plug is not needed.  
         [0015]    [0015]FIG. 2 shows a fragmentary partially sectional longitudinal exploded view of the telescopic shaft of the invention as shown in FIG. 1 c . In this view, the ridges  15  and grooves  17  of the tube  10  and the mating grooves  27  and ridges  25  of the shaft  20  are seen in their locked configuration with their major diameters crossed at right angles to each other. (D B  is parallel to D C ). The centering plug  30  is rotatably attached to the end of the shaft  20  by a spindle or other fastener  35 , so that, when the major diameters of the shaft and tube are parallel, as in FIG. 1 a , the plug  30  keeps the grooves and ridges of the shaft  20  separated from the ridges and grooves of the tube  10 . This centering action allows smooth and easy length adjustment. The shaft may be made from a heavy-walled tube (not shown) to save weight. In that case, the plug fastener would need to provide adaptation for fastening the centering plug to the shaft by any of several well known options.  
         [0016]    [0016]FIGS. 3 a  and  3   b  show an alternative embodiment of the inner shaft member  50  and the outer tube member  40 . In this embodiment, the ridges  55 ,  45  and grooves  57 ,  47  are provided only on the portions of the outer tube  40  and inner shaft  50  which actually interengage when locked. The ends  42  of the outer member  40  in line with the major diameter and the sides  52  of the inner member  50  in line with its minor diameter need not have any ridges and grooves. Thus, the ridges and grooves only appear on the surfaces of the shaft and tube in line with the major diameter of the shaft and the minor diameter of the tube. It is clear from these figures that the inner shaft  50  need not be oval, as shown in FIG. 3A. The sides  52  can be flat so that the shaft has a double D profile as long as it has ridges  55  and grooves  57  at its ends to interengage with grooves  47  and ridges  45  on the sides of the outer tube  40 . The shapes of the inner and outer members can be any which have congruent arcuate cross-sections on which the ridges and Grooves are disposed.  
         [0017]    The methods for making the invention include fully threading the ID of a tube and the OD of a shaft and deforming them both until the major diameter of the shaft is approximately equal to the minor diameter of the tube. The ridges and grooves can be made as separate parallel circumferential forms or a continuous thread. The threads, or alternating grooves and ridges, may be formed by cutting or machining processes, or they may also be formed by rolling or other non-cutting techniques. This would be determined by the equipment available.  
         [0018]    Another method for making the telescopic shaft requires procuring a tube with an oval cross-section and a shaft, which may be hollow, also with an oval cross-section. A circular threading tool, cutting tool, or rolling tool is used to form alternating grooves and ridges on the shaft and tube in line with the major diameter of the former and the minor diameter of the latter. This would have the advantage of minimizing the amount of starting material needed. It would also minimize waste by minimizing the amount of cutting necessary to provide the ridges and grooves on the shaft and tube, in cases where the cutting method is chosen for forming the ridges and grooves.  
         [0019]    In order to prevent turning the shaft or tube through a greater arc than necessary for locking the telescopic shaft length, it would be possible to make the major diameter D C  of the shaft  20  slightly greater than the minor diameter D B  of the tube  10 . This would prevent turning the shaft past the locked position back to an unlocked position, but it could cause jamming of the engaging ridges and grooves if turned too tightly. Another solution is to include an axial key or other discontinuity in the alternating ridges and grooves. The discontinuity can be provided by any axial interruption in the alternating ridges and grooves such as a weld bead or a rolled groove to disrupt the smooth groove/ridge profile. This discontinuity can be provided on either one or both of the members. Since it does not require any additional manufacturing steps, the first option, that of providing a shaft major diameter greater than the tube minor diameter, is preferred.