Abstract:
A bicycle stem assembly comprising a bicycle stem having a novel ways for securing it to an unthreaded bicycle fork steerer tube, the novel means featuring a castellated bushing for pre-loading the upper bearing for the steerer tube and a clamp carried by the stem for selectively locking the stem and bushing to the steerer tube.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to improvements in bicycle handlebar stems and more particularly to an improved assembly for securing a bicycle stem to a bicycle fork steerer tube. 
     DESCRIPTION OF THE PRIOR ART 
     The handlebar of a bicycle is coupled to the bicycle frame by means of a stem having a vertical tube which is secured to the steerer tube of the fork to which the front wheel is attached. Two different approaches have been used extensively for coupling the bicycle handlebar stem to the steerer tube. One approach involves division of an external screw thread on the upper end of the steerer tube onto which is secured the top race of the upper bearing headset assembly, and a lock nut, with the top end of the steering tube terminating flush with or just below the lock nut. With this approach, the vertical tube of the stem is inserted into the steerer tube and carries a threaded fixing stud which in turn carries a wedge nut at its lower end. The fixing stud has a head that is accessible through the top end of the vertical tube of the stem. When the stud is turned, the wedge nut is pulled upwardly against a compensating tapered surface at the lower end of the vertical tube, causing the wedge to be displaced laterally and to tighten against the inner surface of the steerer tube, whereby the stem acts as an extension of the steerer tube. 
     The second approach uses a stem that comprises a dual clamp section that surrounds the steerer tube. In this arrangement, the length of the steerer tube is extended so as to accommodate the clamp section of the stem. The upper race of the upper bearing is not screwed to the steerer tube. In order to permit pre-loading the steering headset bearing, a star nut is located inside the steerer tube, and a preload cap is engaged with the upper end of the steerer tube, and a threaded studs extends through the cap and is screwed into the star nut. Turning the threaded stud varies the force with which the cap forces the stem into engagement with the outer race of the upper bearing headset and thereby determines the pre-loading of the bearing. 
     The first approach is complicated and relatively expensive. The second approach offers the advantage of using a lighter weight stem. However, the second approach suffers from the limitation that it is easy to make a mistake in properly positioning the star nut in the steerer tube, and correcting the mistake is difficult since the star nut, by design, tightly grips the steerer tube. Damage caused by forcing removal of the star nut is especially disadvantageous in the case of expensive light weight bicycle frames. As an alternative to the star nut, a small device which expands radially and has internal threads is inserted into the steerer tube in place of the star nut. The expandable device is more easily removable than the star nut, but it suffers from the disadvantage that it makes a tenuous grip on the steerer tube. 
     A further problem with the foregoing arrangements is that they make it difficult, if not impossible, to pass a brake cable through and out of the upper end of the steerer tube, thus preventing use of the brake assembly invention disclosed in my U.S. Pat. No. 5,803, 207, issued Sep. 8, 1998. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     The primary object of the invention is to provide a new assembly for positively and securely locking a bicycle stem to an unthreaded steerer tube. 
     Another object is to provide a novel stem-securing means which is simple and inexpensive to manufacture and use. 
     Still another object is to provide a bicycle handlebar stem having novel means for securing it to a steerer tube. 
     A further object is to provide a novel bicycle stem/steerer tube combination that facilitates pre-loading of the steerer tube bearings. 
     Another object is to provide a method of attaching a bicycle stem to a steerer tube which facilitates pre-loading of the upper bearing for the steerer tube. 
     A more specific object is to provide an arrangement for securing a stem to a bicycle fork steerer tube that allows a brake cable to extend from brake actuating means carried by the fork up through and out of the upper end of the steerer tube. 
     The foregoing objects are achieved by utilizing with a non-threaded steerer tube a castellated externally-threaded locking bushing that fits onto the upper end of the steerer tube in position to engage the outer race of the upper steering head bearing, and a bicycle stem that comprises a first split clamp section that closely surrounds the tube and is adapted to be compressed into tight engagement with the steerer tube, and a second split clamp section that surrounds and makes a screw thread connection with the castellated bushing and is adapted to be compressed to squeeze the bushing so as to lock it to the steerer tube. The invention includes a method of assembling the stem and bushing with the steerer tube that facilitates pre-loading of the upper bearing associated with the steerer tube. Other features and advantages of the invention are disclosed or rendered obvious by the following detailed specification. 
    
    
     THE DRAWINGS 
     FIG. 1 is a partially exploded fragmentary isometric view of a bicycle frame and fork incorporating a handlebar stem and a locking bushing embodying the invention; 
     FIG. 2 is a fragmentary isometric view from a different angle of the same stem and locking bushing: 
     FIG. 3 is a sectional view of the same stem and locking bushing; 
     FIG. 4 is an enlarged isometric view of the stem and locking bushing; and 
     FIG. 5 is a cross-sectional view of a preferred form of upper bearing assembly for coupling the steerer tube to the bicycle head tube. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, there is shown a portion of a bicycle frame  2  having at its front end an open-ended tubular member  4  (commonly called a “head tube”) which rotatably receives a steerer tube  8  which is an extension of a bicycle wheel- supporting fork member  6 . The fork and the tubular member are coupled by a conventional lower steering head bearing assembly  10  which comprises a first (lower) race  12  that is secured to fork  6  (or the lower end of steerer tube  8 ), and a second (upper) outer race  14  that is secured to the lower end of tubular member  4 . The races of bearing assembly  10  may be affixed, i.e., secured in place, by means well known to persons skilled in the art, e.g., a press fit or a screw connection. Although not shown, it is to be understood that bearing assembly  10  also includes a plurality of ball bearings in a retainer ring that is disposed between the two races  12  and  14 . 
     A second upper bearing assembly  16  is located at the upper end of the tubular member  4 . As illustrated in FIG. 5, the bearing assembly  16  comprises a first (lower) race  18  having a tubular extension  19  that is secured to head tube  4 . This may be done by way of a press-fit, or by a screw thread connection, or by some other means known to persons skilled in the art. The second (upper) race  20  of bearing assembly  16  surrounds the upper end portion  22  of the steerer tube but is not affixed to that tube. Instead it is free to be rotated relative to steerer until it is locked by action of the locking bushing  32  hereinafter described. The inner surface of upper race  20  is tapered to accommodate a tapered centering ring  21  which is split at one point along its circumference so as to allow it to be compressed radially. Bearing assembly  16  also includes a ball bearing/retainer assembly comprising plurality of ball bearings  25  located in holes in a retainer ring  27  that is disposed between the two races  18  and  20 . 
     The illustrated apparatus further includes a novel stem  30  and a castellated threaded locking bushing  32 . Referring to FIGS. 1-4, the stem  30  comprises a body portion  34  having at one end a tubular member  36  for accommodating a typical handlebar  38 . The cylindrical member  36  is split and is provided with a pair of lugs  42 A,  42 B having aligned holes for receiving a screw  40  that is used to draw the lugs together so as to compress the tubular member  36  about the handlebar  38 , thereby locking the handlebar in place. As shown in FIG. 3, the hole in lug  42 B is threaded to mate with the threaded shank of screw  40 . The hole in lug  42 A may but need not be threaded, but is sized so that screw  40  can be rotated therein. 
     The other or rear end of the stem body  34  is provided with a second tubular member  44  which is oriented so that its axis extends at a right angle to the axes of stem body  34  and tubular member  36 . The tubular member  44  is slotted transversely to its axis as shown at  46 , so as to form two clamp sections  48  and  50 . Slot  46  extends through an angle of at least  1800  but less than  3600  along the circumference of tubular member  44 . As seen best in FIGS. 2 and 4, each of these clamp sections in turn is split lengthwise at the “six o&#39;clock” position determined relative to body portion  34 . 
     Each of the clamp sections  48  and  50  is provided with a pair of lugs  52 A,  52 B extending therefrom adjacent where they are split. The lugs  52 A,  52 B of each clamp section have aligned holes for receiving a screw  56 . Although not shown, the holes in lugs  52 A are threaded to make a screw connection with screws  56 . The holes in lugs  52 B may, but need not, be threaded. By turning screws  56  in a given direction it is possible to draw together the lugs  52 A,  52 B of clamp sections  48  and  50 , thereby effectively reducing the inside diameter of those clamp sections. It should be noted that clamp section  48  differs from clamp section  50  in that its inner surface is provided with a screw thread as represented schematically at  62 . The two clamp sections are made so that when they are not compressed by action of screws  56 , their internal diameters are slightly larger than the outer diameter of the upper end of the steerer tube, preferably about 0.005 inch larger. 
     The bushing  32  comprises a hollow body section  64  and a peripheral flange  66 . The body section  64  is cylindrical, while the flange  66  preferably has a polygonal edge configuration (e.g., hexagonal) to permit it to be grasped by a suitable wrench. Bushing  32  is castellated in the sense that its hollow tubular body portion  64  is slit longitudinally at several locations as indicated at  68 . The slits  68  commence at or near flange  66  and extend through the opposite end edge of body section  64 , as seen best in FIG.  4 . Additionally, the exterior surface of the body portion of bushing  32  has a screw thread as represented schematically at  70  in FIG.  4 . Bushing  32  is sized so that its exterior screw thread  70  will make a loose screw connection with the internal screw thread  62  of clamp section  48  when the latter is in its uncompressed condition, i.e., when its screw  56  in lug  52 B is completely, or nearly completely, unscrewed from lug  52 A. 
     How the handlebar stem and the locking bushing are assembled onto and secured to the steerer tube so as to achieve selective preloading of the upper bearing assembly will now be described. Assume that steerer tube  8  is disposed in head tube  4  as shown in FIG. 1, with the two races of bearing  10  secured in place as previously described, the lower race  18  of bearing  16  secured to head tube  4 , and the upper race  20  and the centering ring  21  surrounding but not secured to steerer tube  8 . With both of the screws  56  backed off so that the clamp section  48  is expanded enough to accommodate and make a screw connection with bushing  32  and clamp section  50  is large enough to make a close sliding fit on the upper end of the steerer tube, bushing  32  is screwed substantially all the way into clamp section  48 . Then, with the bushing in place, stem  30  is slipped onto the steerer tube  22  so that clamp section  50  surrounds the upper end of the steerer tube and the flange  66  of the bushing lies close to or lightly engages the upper race  20  of the upper bearing assembly  16 . Then the screw  56  of clamp section  50  is turned so as to cause that clamp section to be drawn into tight clamping relation with the upper end  22  of steerer tube  8 . Thereafter, bushing  32  is rotated in a direction to move it away from clamp section  50 . As the bushing is backed out of clamp section  48 , its flange  66  forces centering ring  21  to exert a downward pressure on the upper race  20  of bearing assembly  16 . Centering ring  21  functions to (a) locate the race  20  radially relative to the steerer tube so that the steerer tube is centered relative to that race and (b) also apply an axial preload to bearing  16 . The axial pressure applied to the centering ring compresses it down onto the mating taper of the inner surface of race  20 , and also radially inward to firmly grip the steerer tube, much like a collet functions. The bushing&#39;s position is adjusted so that it exerts a suitable load on bearing assembly  16  that is calculated to eliminate or acceptably minimize axial play of the steerer tube in the frame&#39;s head tube  4 . Once the desired bearing preloading is achieved, the screw  56  of clamp section  48  is turned in a direction to compress that clamp section radially inward to an extent that compresses the castellated body portion  64  of the bushing into a gripping and locking relations with the steerer tube, with the result that the preload applied to the upper bearing assembly by the bushing will remain fixed. 
     The foregoing design offers a number of advantages. For one thing, it is simpler than prior arrangements that are designed to permit adjustable preloading of the steerer tube bearing assemblies. Another advantage is that it avoids possible damage to the steerer tube as can occur when using a star nut. It also does not require the steerer tube to be threaded. Additionally, the preloading of the bearing assembly is easily adjusted, requiring in turn only loosening of the screw  56  associated with clamp section  148 , rotation of bushing  32 , and then re-tightening the screw  56 . Another important advantage is that the interior of the steerer tube remains unobstructed, so that it is now possible to pass a brake cable through and out of the upper end of the steerer tube, thereby making it possible to use brake assemblies as disclosed in my U.S. Pat. No. 5,803,207, issued Sep. 8, 1998. 
     Still another advantage is that it is not necessary to cut the steerer tube to a predetermined length, as is required with prior systems. This invention allows the stem to be moved up or down within limits on the steerer tube, while still allowing the castellated bushing to provide desired preloading of the bearings. The new stem architecture further offers the advantage of reduced cost because of its simplicity. Of additional benefit is the fact that bearings  10  and  16  are of conventional design. Still other advantages will be obvious to persons skilled in the art from the foregoing description and the drawings. 
     Obviously the apparatus as shown in the drawings may be modified without departing from the spirit of the invention, for example, the two clamp members  48  and  50  may be formed as separate members and welded to the stem body  34 , rather than constituting portions of a common cylinder. Additionally, the lugs  42 A,  42 B (and also the lugs  52 A,  52 B) may be coupled together by a screw and nut arrangement, thereby eliminating the need to a threaded hole in one or both lugs. Similarly, the tubular member  36  at the front end of the stem body  34  also may be modified without affecting the mode of attachment of the stem to the steerer tube. Also various forms of angular contact bearings that require some axial preload to function properly may be used as the lower and upper bearings  10  and  16 . Still other modifications will be obvious to persons skilled in the art.