GB2179103A

GB2179103A - Improvements in bicycles

Info

Publication number: GB2179103A
Application number: GB08520561A
Authority: GB
Inventors: Francis George Kirk
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-08-16
Filing date: 1985-08-16
Publication date: 1987-02-25
Also published as: GB8520561D0; GB2179103B

Abstract

A front derailleur includes a laterally movable chain guide 12 mounted on a saddle stem above a crank bearing, and an operating cable 13 for the chain guide 12. The cable 13 includes a core 13a and a cover 13b. The core 13a is connected to an operating lever 14 and an abutment 16 fixed on the frame, and the cover 13b is anchored at one end to a point 26 on the frame and passes in an arc generally downwardly to a fitting 23 for operating a lever 21 forming part of the operating linkage for the chain guide 12, whereby the cover 13b operates on the linkage to move the chain guide 12 when the core 13a is tensioned. The invention is particularly applicable to a bicycle having a frame cast in magnesium and including a lower bar interconnecting a head and a saddle stem and connected to the saddle stem at a point significantly above a crank bearing. The chain guide is mounted to the saddle stem between the crank bearing and the intersection with the lower bar, the operating cable 13 being arranged to run parallel with the lower bar, and the forward end of the cover 13b being anchored thereto somewhat forward from the intersection with the saddle stem. <IMAGE>

Description

SPECIFICATION Improvements in bicycles This invention relates generally to bicycles and in particular to an improved arrangement for a derailleur speed change gear.

Derailleur speed change gears are in two forms, and many bicycles are fitted with both.

A rear derailleur has a multiple drive sprocket on the rear wheel, and the conventional drive chain is shifted laterally between the sprockets to effect the gear change. A front derailleur has a multiple, normally double, crank wheel, and the chain is shifted laterally between the crank wheels to effect the gear change. In either case, a chain-tensioning jockey arm is provided.

Conventionally, the derailleur gear is operated by a laterally movable chain guide which is controlled by a cable. For a front derailleur, the cable runs down a frame lower tube or member to a point near the crank bearing, and then turns upwardly to the location of the chain guide adjacent the top of the crank wheel. Normally, the chain guide is spring biased in one direction and pulled by the cable tension in the other. Usually, a form of parallelogram linkage is used to convert the movement of one end of the cable into a lateral movement of the chain guide.

In my as yet unpublished Patent application 8423272, there is described and shown a form of bicycle frame which is cast in magnesium or an alloy thereof. In the arrangement shown in that application, the lower tube interconnecting the head and saddle stem does not intersect the saddle stem in the region of the crank bearing, but at an intermediate point above the level of the top of the crank wheel.

Accordingly, the geometry is such that the cable for operating a conventional front derailleur cannot easily follow a path such that it passes down the lower bar and then upwardly in a natural loop to the location of the chain guide control.

In accordance with the present invention, there is provided a bicycle having a frame, which may be cast from magnesium or an alloy thereof, including a saddle stem and a crank bearing, a front derailleur including a laterally movable chain guide mounted on the saddle stem above the crank bearing, an operating cable for the chain guide, the said cable including a core and a cover, in which the core is connected to an operating lever and a point fixed on the frame, and the cover is anchored at one end to a point on the frame and passes in an arc to a connection to operating linkage for the chain guide, whereby the cover operates on the linkage to move the chain guide when the core is tensioned.

By using the cover or cable outer as the operating element of the cable, the geometry may be adapted to allow the cable to be led in from above, without major adaptation to the operating linkage.

In a particular arrangement, the frame includes a lower bar interconnecting a head and a saddle stem and connected to the saddle stem at a point significantly above a crank bearing, and the chain guide is mounted to the saddle stem between the crank bearing and the intersection with the lower bar, the operating cable being arranged to run parallel with the lower bar, and the cover being anchored thereto. The cover may be anchored to a point on the lower bar somewhat forward from the intersection with the saddle stem.

The invention will be further described with reference to the accompanying diagrammatic drawings, in which, Figure 1 is a side elevation of a preferred form of bicycle in accordance with the invention; Figure 2 is a view to a larger scale illustrating a preferred arrangement of cable and linkage; and Figure 3 is a view similar to Fig. 2 and showing the parts in a different operated position.

The bicycle shown in Fig. 1 has a cast frame including a saddle stem 1 and a head 2 interconnected by a cross bar 3 and a lower bar 4. A structural bridge 5 interconnects the cross bar 3 and lower bar 4 at an intermediate location. The bicycle is illustrated as having a rear derailleur with a multiple sprocket 6 and a laterally movable chain guide 7 operated by means of a cable 8 controlled by a lever 9. A front derailleur has a double crank wheel 11, and is operated by a laterally movable chain guide 12 controlled by a Bowden cable, indicated generally by the reference numeral 13, worked by a lever 14. The levers 9 and 14 are mounted close together on the lower bar 4.

Reference will now be made more particularly to Figs. 2 and 3 for a more detailed description of the invention. The parallelogram, linkage 15 for the chain guide 12 is shown in detail. The chain guide 12 is pivoted to one end of a lever 21 rockable about a fixed pivot axis 22, and having its other end pivoted to a fitting 23 on the movable end of the cable outer 13b. The movement of the chain guide 12 is further controlled by its being pivoted to a link 24 rocking about a fixed pivot axis 25.

The link completes the parallelogram linkage.

The linkage is biased by a spring (not shown) acting on the lever 21 towards the position of Fig. 2.

It will be seen that the cable 13 is led into the linkage 15 for the chain guide 12 from above, instead of from below as would be normal if the lower bar were connected to the saddle stem in the region of the crank bearing instead of at the much higher position shown.

In order to achieve this, without the need for reversal of the operation of the linkage, the operation of the cable 13 is reversed. A core 1 3a is connected at the forward end to a movable part of the lever 14 and at the rearward end to a fixed abutment adjacent the linkage. A comparatively short cover 1 3b for the cable 13 is anchored at its forward end to an abutment 26 at a point on the lower bar 4 just forward of the intersection with the saddle stem 1.

The cover 13b, with the core 1 3a inside it, then extends in a generally downwardly directed arc to a connection with the movable fitting 23 forming part of the linkage 15.

When the core 1 3a is tensioned using the lever 14, the arc tends to straighten to the position shown in Fig. 3, and thus causes the distal end of the cover 13b to press on and move the fitting 23 and operate the lever 21 against the action of the spring. It will be seen that in Fig. 3, the fitting 23 is shown much nearer the fixed abutment 16.

In the reverse direction, the spring tends to return the arc to the original form when the cable is released from tension.

Claims

1. A bicycle having a frame including a saddle stem and a crank bearing, a front derailleur including a laterally movable chain guide mounted on the saddle stem above the crank bearing, an operating cable for the chain guide, the said cable including a core and a cover, in which the core is connected to an operating lever and a point fixed on the frame, and the cover is anchored at one end to a point on the frame and passes in an arc to a connection to operating linkage for the chain guide, whereby the cover operates on the linkage to move the chain guide when the core is tensioned.

2. A bicycle as claimed in claim 1, in which the frame includes a lower bar interconnecting a head and a saddle stem and connected to the saddle stem at a point significantly above a crank bearing, and in which the chain guide is mounted to the saddle stem between the crank bearing and the intersection with the lower bar, the operating cable being arranged to run parallel with the lower bar, and the cover being anchored thereto.

3. A bicycle as claimed in preceding claim 1 or 2, in which the arc in the cable cover extends generally downwardly towards the operating linkage.

3. A bicycle as claimed in claim 2, in which the cover is anchored to a point on the lower bar somewhat forward from the inersection with the saddle stem.

4. A bicycle as claimed in any of the preceding claims, in which the arc in the cable cover extends generally downwardly towards the operating linkage.

5. A bicycle as claimed in any of the preceding claims, in which the frame is cast from magnesium or an alloy thereof.

6. A bicycle substantially as hereinbefore described with reference to the accompanying drawings.

CLAIMS Amendments to the claims have been filed, and have the following effect: Claims 1 to 4 above have been deleted or textually amended.

New or textually amended claims have been filed as follows: Claims 5 & 6 above have been re-numbered as 4 & 5

1. A bicycle having a frame including a head, a saddle stem and a lower bar interconnecting the head and the saddle stem and connected to the saddle stem at a point significantly above a crank bearing at the lower end thereof, a front derailleur including a laterally movable chain guide mounted on the saddle stem between the crank bearing and the inersection with the lower bar, an operating cable for the chain guide, the said cable including a core and a cover, in which the core runs generally parallel with the lower bar and is connected to an operating lever and a point fixed on the frame, and the cover is anchored at one end to the lower bar and passes in an arc to a connection to operating linkage for the chain guide, whereby the cover operates on the linkage to move the chain guide when the core is tensioned.

2. A bicycle as claimed in claim 1, in which the cover is anchored to a point on the lower bar somewhat forward from the intersection with the saddle stem.