BICYCLE FRAME AND BICYCLE

Abstract: A bicycle frame is cast in soft material, such as magnesium, and has at least one location 8 to receive a replaceable bearing or other component. The location 8 is constituted by a replaceable steel sleeve 9 which is a push fit in the frame and is secured by adhesive which is strong enough to hold the sleeve 9 during normal operation but may be softened by heat (e.g. to 200°C) to enable the sleeve 9 to be replaced when required. The sleeve 9 may have threads cut therein in the case of the crank bearing location illustrated in figure 2, but in other cases, such as steering bearings, a smooth surface for a push fit may be more appropri­ ate. The invention is also applicable to the provision of a sleeve liner for a saddle stem.

Description: BICYCLE FRAME AND BICYCLE This invention relates to bicycle frames. A bicycle frame conventionally includes a bottom bracket to which are connected the rear forks, the saddle stem and a lower tube. The bottom bracket also acts as a housing for a crank bearing. A steering bearing is housed in a steering tube (or head) which interconnects the lower tube and an upper tube (in a lady's bicycle) or a cross bar. In published patent application GB-A-2136745, there is shown and described a bicycle frame which is cast in magnesium or other light metal or alloy. This also includes cast-in locations for crank and steering bearings. The steering bearing is normally formed by an assembly which includes short tubes which are a push fit into the steering tube. The crank bearing is usually retained in the bottom bracket by means of a threaded engagement onto threads, which are not necessarily continuous, cut in the bottom bracket. When a bicycle is subjected to heavy use, the crank and steering bearings tend to need replacement at intervals. This entails removal, frequently by unskilled amateurs without the proper tools, of the old bearing and introduction of the new. During this process, the threads in the bottom bracket, or the surfaces needing to make an accurate push fit for the steering bracket, may become damaged. In many such cases, the damage may be irreparable, so the frame has to be scrapped. In accordance with one aspect of the present invention, there is provided a bicycle frame having at least one location to receive a replaceable component such as a bearing, in which the said at least one location is constituted by a sleeve which is set in the frame and secured by adhesive, and wherein the adhesive is strong enough to hold the sleeve durang normal operation but is susceptible of softening to enable the sleeve to be replaced when required. The invention is particularly suited to a frame which is cast in magnesium or an alloy, and in such a case, the sleeve may be of steel. A bicycle frame conventionally includes a saddle stem which has an expandable open tubular upper end which receives a saddle support tube and is clamped thereover to secure the saddle in an adjusted position. The saddle support tube is normally a tight sliding or interference fit in the upper end of the saddle stem, so that some fairly vigorous effort is required to move the support tube to the required adjusted position, particularly if the position has not been adjusted for some conslderable time. When the saddle position Is adjusted In a cast magnesium bicycle frame, or when the saddle is replaced, the inner surface of the open upper end of the cast magnesium saddle stem may become damaged by the movement of the saddle support tube, particularly if the latter is removed completely and re-introduced. In many such cases, the damage may be irreparable, so the frame has to be scrapped. Also, the saddle support tube is frequently of aluminium, and the current fashion is for this to have external flutes, which have a largely aesthetic, rather than technical, effect. These flutes do not extend the full length of the support tube. They have the effect of allowing a small amount of water to enter the open top of the saddle stem and become trapped between the support tube and the interior of the saddle stem. This water may set up electrolytic corrosion by forming an electrolytic cell in conjunction with the magnesium of the frame and the aluminium of the saddle support tube. In accordance with another aspect of the present invention, there is provided a cast bicycle frame having a saddle stem with a cast-in open upper end to receive a saddle support tube so as to be clamped thereover, in which the said open upper end is provided with a liner sleeve, preferably of aluminium, which is set in the open upper end and secured by adhesive, and wherein the adhesive is strong enough to hold the liner sleeve during normal operation but is susceptible of softening to enable the liner sleeve to be replaced when required. In view of its considerable length, this liner sleeve is preferably an easy push fit in the frame at working temperatures. It is preferred to use one of the modern ultra-strong adhesives in order to achieve the required strength, and to choose one that softens when heated, e.g. by a radio frequency heater, to a temperature above the normal working temperature of the bearing, say 200 C. A suitable adhesive would be LOCTITE (Registered Trade Mark) 601. It will however be understood that the invention is not limited to cast magnesium frames, but may also be applied to more conventional forms of frame. The sleeve may have threads cut therein, or it may be smooth to receive bearing parts as a push or interference fit. The sleeve or sleeve liner may be a push fit in the frame at normal ambient temperatures, and the release of the sleeve by softening the adhesive by heating may be enhanced by differential thermal expansion between the sleeve or sleeve liner and the surrounding metal. The invention further comprises a bicycle comprising a frame in accordance with the invention as set forth above. The invention will be further described with reference to the accompanying drawings, in which; Figure 1 is a side elevation of a cast bicycle frame to which the invention is applied; Figure 2 is a section on the line II-II of figure 1; Figure 3 is a section on the line III-III of figure 1 omitting an insert; Figure 4-is a partial elevation on the arrow IV of figure 1; Figure 5 is an elevation of an insert; and Figure 6 is a section on the line VI-VI of figure 1. The cast magnesium bicycle frame illustrated Is of a type generally described in the above-mentioned published application, and Includes a cross bar 1 of I section with lightening holes 2, a lower bar 3 of C section closed by a second casting forming a panel 4, a tubular head 5 and a saddle stem 6 of V section with lightening holes 7. The lower bar 3 joins the saddle stem 6 at an intermediate# position, well above a location 8, replacing a bottom bracket, to receive a crank bearing. The location 8 is pressure die-cast in magnesium, with the rest of the frame, but in order to make it durable enough to allow removal and replacement of the crank bearing, there is provided a steel liner 9 (see also figure 2) which is a push fit and is secured by an ultra-strong adhesive which can be softened by application of localised heat, e.g. by an KF heater, to enable replacemeilt of the liner in the event it becomes damaged in use. The differential thermal expansion as between the steel liner 9 and the magnesium location 8 further assists in loosening the liner 9 for easy removal. The steel liner 9 has threads cut in it to secure the crank bearing. The head 5 provides a location at each end for a short tubular bearing part push-fitted therein, and for this purpose, it has slightly enlarged end parts 5a linked by tapering parts 5b to the main length of the head 5. Figure 3 shows the shape of the enlarged end parts 5a. In order to enable the replacement of the steering bearing assembly, without damage to the magnesium of the head 5, there is provided in each enlarged end part 5a of the head 5, a push -fitted steel liner 11 (see also figures 4 and 5) with an end flange 12. This liner 11 is also secured by an ultra-strong adhesive which can be softened by application of localised heat, e.g. by an RF heater, to enable the ready replacement of the liner 11. The saddle stem 6 has an upper part 21 provided with a upwardly open tubular portion 22 to receive a conventional saddle support tube (not shown), which Is normally of aluminium. In order to make upper portion 22 of the saddle stem 6 durable enough to allow removal and replacement of the saddle support tube, and also to protect it against electrolytic corrosion, it is provided with an aluminium liner sleeve 23 (see also figure 6) which is an easy push fit and is secured by an ultra-strong adhesive which can be softened by application of localised heat to enable replacement of the liner sleeve 23 in the event it becomes damaged in use. The differential thermal expansion as between the aluminium liner sleeve 23 and the magnesium of the saddle stem 7 further assists in loosening the liner sleeve 23 for easy removal. The presence of the liner sleeve 23 in the tubular portion 22 also seals the tubular portion 22 against ingress of water. Various modifications may be made within the scope of the invention.

Claims: CLAIMS 1. A bicycle frame having at least one location (8,21) to receive a replaceable component, characterised in that the said at least one location (8,21) is constituted by a sleeve (9,11,23) which is set in the frame and secured by adhesive, and wherein the adhesive is strong enough to hold-the sleeve (9,11,23) during normal operation but is susceptible of softening to enable the sleeve (9,11,23) to be replaced when required. 2. A cast bicycle frame having a saddle stems (6) with a cast-in open upper end (22) to receive a saddle support tube so as to be clamped thereover, characterised in that the said open upper end (22) is provided with a liner sleeve (23) which is set in the open upper end (22) and secured by adhesive, and wherein the adhesive is strong enough to hold the liner sleeve (9,11,23) during normal operation but is susceptible of softening to enable the liner sleeve (23) to be replaced when required. 3. A bicycle frame according to claim 1 or 2, characterised in that the frame is cast in magnesium or an alloy thereof. 4. A bicycle frame according to claim 3, characterised in that the sleeve (9,11,23) is of steel. 5. A bicycle according to any of claims 1 to 4, characterised in that the sleeve (9,11,23) has threads cut therein. 6. A bicycle frame according to any of the preceding claims, characterised in that the sleeve (9,11) or sleeve liner (23) is a push fit in the frame at normal ambient temperatures. 7. A bicycle according to claim 2, characterised in that the liner sleeve (23) is of aluminium. 8. A bicycle frame according to claim 7, characterised in that the sleeve (23) liner is an easy push fit in the upper end (22) of the saddle stem (6). 9. A bicycle frame according to any of the preceding claims, characterised in that the adhesive is softenable by heating to a temperature in the region of 200 C. 10. A bicycle having a frame according to any of the preceding claims.

Inventors: KIRK, FRANCIS GEORGE
Applicants: KIRK, FRANCIS GEORGE
Application year: 1986
Main classification: B62K19
IPC codes: B62K19, F16C33, F16C35