GB2607032A

GB2607032A - A bicycle frame and fork

Info

Publication number: GB2607032A
Application number: GB2107407.5A
Authority: GB
Inventors: Carey Charles
Original assignee: Individual
Current assignee: Individual
Priority date: 2021-05-25
Filing date: 2021-05-25
Publication date: 2022-11-30
Anticipated expiration: 2041-05-25
Also published as: GB202107407D0; GB2607032B

Abstract

A bicycle has a single strut 1 connecting the handlebars 6 and the front wheel 9 positioned on one side of the bicycle, a crossbar 2 from above the front wheel 9 to a position at the bottom of the frame where the pedals are located 11, a single strut 3 connecting the back wheel 9 to the crossbar 2 positioned at the opposite side of the bicycle to the front strut 1, and a another strut 4 from the position of the pedals 11 to support the saddle 7. The strut 3 connecting the back wheel to the frame holds the drivetrain (25, figure 5).

Description

Bicycle frames and forks are typically characterised by a plurality of metal tubes and wheel hub brackets that are joined by welding, soldering or brazing. The process requires jigs to hold the tubes and brackets in position and the manufacturing process is labour intensive. Furthermore the metal tubes, typically steel or aluminium, require extensive preparation prior to joining such as bending, hydroforming, and complex cutting with edge preparation. In order to keep costs to acceptable levels, the majority of bicycle frames are made in low labour cost countries where there is a skilled labour force.

Attempts have been made to design less labour intensive bicycle forks and frames, using manufacturing methods such as plastic injection moulding, metal casting and metal stamping. However these processes require extensive and costly tooling; furthermore these processes do not lend themselves to producing frame designs in different sizes. Another disadvantage of using these processes is that frequently they result in frames of insufficient strength and rigidity, or alternatively, excessive weight.

This invention describes a fork and frame design which requires minimum labour costs to manufacture. The fork and frame are monoblades, where the front and rear wheels are cantilevered from single frame elements that support each wheel. In contrast to previous monoblade bicycle designs, there is a minimum of tooling and tube preparation which further reduces manufacturing costs. A feature of the invention is that frame elements can be joined by either welding, or alternatively, using fasteners such as bolts. This permits fork and frame manufacture to be part of the bicyde assembly process which can be undertaken by a less skilled labour force and requires less tooling investment.

One embodiment of the invention is to use aluminium extrusions for the fork and frame. Each extrusion has a plurality of holes which can be undertaken by laser cutting. This has the advantage that no tooling is required and different designs can be readily implemented by changing the laser cutting software programme. The fork comprises a single straight extrusion which requires no further bending or hydroforming, and the extrusion may be configured to also support the handlebars, avoiding the need for handlebar stems. The extrusion can also support the wheel bearings with bearing housings attached to the extrusion walls. The frame comprises three extrusions bolted or welded together. The rear monoblade extrusion houses the drive mechanism which can be either a shaft drive, spur gears, or a chain or belt drive. A gear mechanism can be provided that may be based on the derailleur design or alternative designs. Both the fork and rear monoblade can house the braking system such as a disc brake, roller brake, or band brake design. With such a configuration the braking system is fully protected from rain and dirt. In addition, either front, or rear, or both, monoblades can house an electrical generator or dynamo for lighting and other purposes such as electrical bike locking. A feature of such an arrangement is that the assembly of many components can be achieved using the end openings of the extruded profile thereby avoiding large openings in the side wall which reduces the torsional strength of the fork and frame members as well as adding further tooling and assembly cost. Assembly can be aided by use of preassembled components on jigs and fixtures which are then inserted into the frame. Said jigs and fixtures can either be removed or permanently left in the frame to help future bicycle maintenance disassembly. Furthermore the hollow sections in the fork and frame provide space for housing batteries, motor, and electronics in an electric bicycle, thereby requiring minimal change to the design. Another embodiment of the invention is to use straight tubes from welded or drawn sheet steel or alternatively to use composite tubing such as carbon fibre.

With a straight monoblade supporting the front wheel, the steering mechanism, comprising bearings mounted along an axis that lies in the centre plane of the bicycle, will be offset from the axis of the monoblade tube. The fork monoblade and frame downtube are consequently provided with brackets and the bearing can be a simple plain bearing comprising a shaft and housing. A design that allows simple alignment between the two steering bearings can be achieved by the provision of a single shaft.

A feature of the design is that alternative brake and gear change activation mechanisms can be provided in contrast to the traditional cable operation which is attached to handlebar mounted brake and gear change levers. This is possible because such activation mechanisms can be protected from damage and rain and dirt, because of the protection provided by the enclosed monoblade housings. Front and rear brakes can be of the band brake configuration where the front brake can be activated by twisting the handlebars and the rear brake can be activated by using a foot engaging an externally mounted actuator on the rear monoblade. Similarly a derailleur gear change mechanism can also be operated by a foot engaging with a secondary actuator mounted on the rear monoblade.

Referring to the drawings, Figure 1 shows two elevation views of the bicycle with certain features like pedals and pedal cranks, removed for clarity. The fork comprises a single straight monoblade extrusion 1. The frame comprises a down tube formed by a straight extrusion 2, a rear monoblade formed by a straight extrusion 3, a seat tube formed by a straight extrusion 4, and a boss 5 to hold one of the bearings for the bottom bracket spindle 11. The fork 1 supports the handlebars 6 and the seat tube 4 supports the saddle tube 8 that is attached to the saddle 7. The fork 1, and frame rear monoblade 3, support the bearings for the wheel hubs 10 and wheels 9 in suitably mounted bearing housings on the extrusion side walls.

Figure 2 shows a plan view with certain features like the saddle, removed for clarity. The pedals 12 and pedal cranks 13 are shown in addition to the centreline of the bike 14. It can be seen how the straight fork 1, and frame down tube 2, are both off centre to the centreline 14. The fork steering axis bearings are positioned on the centreline and are attached to the fork and down tube by provision of suitable brackets. The boss 5 holds one of the bearings for the bottom bracket spindle and provides suitable width to position the pedal cranks 13 equally from the bicycle centreline 14. Both front and rear wheel can be dished to reduce the width of the wheel on the monoblade side in order to minimise the monoblade offset from the centreline 14. This reduces loading and bending forces in the fork and frame. The fork and frame extrusions are hollow and have large flat sides such as a rectangular profile with radiused corners. This provides a more efficient section to resist lateral loads on the fork and frame in addition to providing surfaces for the three frame tubes to align to each other thereby minimising tooling required for frame alignment. The frame down tube 2 can be made wide enough to overlap the bicycle centreline 14 such that the steering bearing arrangement can be housed in the tube.

Figure 3 shows a bearing arrangement for the bicycle for the wheels and bottom bracket spindle. The wheel bearings 15 are held in housings which are attached to the walls of the hollow monoblade sections 1 and 3. This arrangement permits the wheel hubs 16 to pass into the hollow monoblades thereby providing the opportunity to have a fully enclosed braking system in the fork and frame structure which is protected from rain and dirt increasing the life of the braking system and reducing maintenance. Such a system may be a disc brake, roller brake, band brake or other design. The enclosed wheel hubs 16 may also provide space for provision of an electrical generator or dynamo for bicycle lighting and other services such as an electronic bike lock.

The bottom bracket spindle bearings 17 support the bottom bracket spindle 18. One of the bearings is held in a housing which is attached to the outer wall of the hollow section frame monoblade 3. This arrangement permits the drive mechanism such as a chain wheel 19, to be positioned in between the bearings 17, thereby reducing the load on the bearings and providing a rigid mounting. Thus the frame monoblade has a very rigid drive train system with a chain wheel 19, chain 20, and sprocket 21 all mounted between bearings significantly reducing bearing load and drive train deflection. Furthermore the whole assembly can be preinstalled in the frame monoblade 3 prior to attaching to the rest of the frame. This is particularly attractive in a frame that is held together with fasteners.

Figure 4 shows a drive train arrangement comprising a chainwheel 19, a reduction gear shaft 22, a freewheel block with three gear sprockets 23, and a chain tensioner mechanism 24, all housed in the frame monoblade 3. The derailleur gear change mechanism is not shown. Such an arrangement permits a lower profile hollow section as the chain wheel 19, can be made a smaller diameter while providing the same gear ratio as an arrangement without the reduction gear shaft 22.

Figure 5 shows the assembly of the drive train where all components are mounted on a jig fixture plate 25, which is then inserted through the profile opening of the rear monoblade 3. This avoids the need for additional openings in the extrusion for assembly purposes which add costs and reduce the strength and rigidity of the monoblade. The plate 25 may be removed after assembly or alternatively, left in the monoblade in order to help future maintenance or replacement of parts. The assembly process is completed with suitable plugs on both openings, one of which can be integrated with a rear light.

Figure 6 shows two arrangements for the bottom bracket spindle. In one of these arrangements the bottom bracket spindle comprises two parts and torque is transmitted from the pedal cranks 13 by means of 3 shear face couplings 26, the whole assembly being clamped by means of one or more bolts passing through the pedal cranks. In the second arrangement, the bottom bracket spindle is a single piece and torque is transferred by means of spline couplings 27, in the pedal cranks. The spindle may comprise a fully splined shaft passing through the bearing inner races and chain wheel.

Figure 7 shows a known band brake configuration comprising a braking drum 28 and braking band 29 housed in the front monoblade housing and mounted on the wheel hub 10 which extends into the monoblade. The band is activated by an element 30 which is attached to the band 29 and the handlebars 6. The element 30 is pulled by twisting the handlebars about their axis, said handlebars being mounted in the monoblade and provided with suitable bearings mounted on the monoblade to enable rotation. The element 30 can be a continuation of the band 29 and can be directly wrapped around the handlebars 6.

Figure 8 shows a similar band brake arrangement mounted on the rear wheel where the band 29 is attached to a lever 31 that rotates around a pivot member 32 that is fixed to the monoblade. The band 29 is tightened around the braking drum 28 by depressing the lever 31, pushing on an element 33 that protrudes the monoblade and is activated by the foot. A similar arrangement of levers can be provided to activate a gear change mechanism such as a derailleur, thereby avoiding cables which add complexity of the bicycle.

Figure 9 shows the steering mechanism which comprises bearing brackets 35 mounted on the front monoblade 1 and bearing brackets 36 mounted on the frame down tube 2. The bearing load between the top and bottom pair of brackets is transferred by means of a shaft which if made as a single continuous element 37 provides a simplified means of aligning the brackets during assembly before they are fixed to the monoblade and down tube respectively.

Claims

Claims 1. A bicycle where both front and rear wheels are respectively supported by a structure which comprises a single monoblade which is straight over its full length, the front monoblade being provided with suitable brackets for the steering bearings, and the rear monoblade housing part of the bottom bracket mechanism.
2. A bicycle according to Claim1, where the rear wheel drivetrain is housed in the rear monoblade and assembled from the end openings of the straight monoblade.
3. A bicycle according to Claim 2, where assembly is aided by a jig or fixture which locates components relative to each other, prior to insertion into the tubular monoblade, said jig or fixture being either removed after assembly or alternatively, left in the monoblade to assist future maintenance or component replacement.
4. A bicycle according to Claim1, where the handlebar is mounted directly on the front monoblade.
5. A bicycle according to Claim1, where the wheel bearings are mounted on the font monoblade such that the wheel hub extends into the monoblade to provide provision for an enclosed braking system.
6. A bicycle according to Claim 1, where the front brake is activated by twisting the handlebars.
7. A bicycle according to Claim 1, where the rear brake and gear change are activated by the foot engaging with appropriately mounted external actuators on the rear monoblade.
8. A bicycle fork and frame according to Claim1, with a bottom bracket spindle comprising at least two shear face couplings between pedal cranks and spindle.
9. A bicycle fork and frame according to Claim1, for use in a folding bike, or children's bike, or electrically assisted bike or cargo bike.