GB2038736A - Resilient suspension of cycle wheels - Google Patents

Abstract

The driven wheel 46 of a cycle is mounted on a sub-frame 48, 52 which, in turn, is mounted on the main frame 10 of the cycle for pivotal movement about the axis of the pedal crank spindle, a leaf spring 50 acting between the sub-frame and main frame. The steerable wheel 22 of the cycle is mounted in a fork assembly 24 which is offset from the steering column shaft and is connected to the latter by a parallelogrammic linkage comprising upper and lower pairs of links 28, 30, the links of each pair being rigidly connected together by a crosspiece and one or more springs 36 being arranged to act diagonally across the parallelogram. <IMAGE>

Description

SPECIFICATION Cycles This invention relates to cycles, and more particularly to the spring suspension of cycle frames especially (but not exclusively) for pedal bicycles.

In accordance with a first aspect of the invention a cycle frame journals a transverse shaft which forms an element in the drive transmission of the cycle, and the driven wheel is carried in a sub-frame which is pivoted on the axis of said shaft, resilient means being provided for urging the sub-frame to a predetermined range of positions relative to the frame.

When the cycle is a pedal bicycle, the shaft will be the spindle which carries the pedal cranks and which isjournalled in the bottom bracket of the frame; and the sub-frame, comprising the chain-stays will be journalled on the bottom bracket. Hence, when the chain-stays pivot in suspension movement, the distance between centres of the spindle and the driven wheel axle (rear wheel spindle) remains constant, and therefore chain tension also remains constant.

The resilient means may comprise a leaf spring, or leaf spring set fixed at one end near to the bottom bracket, e.g. to the seat pillar tube of the frame, and fixed at the other end to a sub-frame element so that in pivotal movement of the sub-frame, the spring is stressed or recovers (according to the direction of movement). The said sub-frame element may be analogous to the seat-stays of a conventional (rigid) diamond frame, but extending only from near the rear wheel spindle towards the saddle but free of connection (except to the leaf spring) at the saddle end.

In accordance with a second aspect of the invention, front suspension for a cycle comprises girder forks mounting the front and stearable wheel, the girders being connected in parallelogram linkage fashion to the steering column, with spring means extending diagonally across the parallelogram to provide resilient suspension, and characterised in that the links between the girder and column on one side of the forks are rigidly connected to the corresponding links on the other side of the fork.

Preferably a pair of links and the rigid connection therebetween form an H shaped assembly where each upright of the H is a link.

This feature reduces the possibility of relative movement of the girders whilst avoiding the need for large bearing surfaces at the link pivots.

According to a further feature, the front suspension resilient means comprises one or more generally helical or spirally would springs extending generally diagonally across the parallelogram, with each end of each spring coupled to the parallelogram through the length of the spring, so that when two points adjacent opposite ends of the spring move away from one another in suspension movement, the spring is shortened. This enables compression springs to be used (as distinct from tension springs) and these have the advantage that the coil-bound condition provides a positive limitation to movement at the end of the intended spring travel.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure lisa side view of a pedal bicycle in accordance with the invention; and Figure 2 is an enlarged fragmentary view of the front suspension of the cycle.

Referring now to the drawings, the cycle comprises a main frame defined by top tube 10, seal pillar tube 12, steering column 14 and bracing tube 16. At the foot of the seat tube 12 there is a bottom bracket 18 which journals the pedal spindle (not shown) carrying pedal cranks 20.

The steering column 14 journals a generally vertical shaft (not shown) about which the front wheel 22 can be turned for steering purposes. The front wheel is mounted in girder fork 24 connected to the steering column shaft via a pair of transversely spaced intermediate shafts 26 and a parallelogrammic linkage which comprises upper and lower pair of links 28,30 respectively, the arrangement being such that when the front wheel is in the straight ahead position, the girder fork tubes 24, the shafts 26, and the links 28,30 are disposed in two sets, one on each side of a medial plane to the steering column shaft.

The shafts 26 are rigidly connected to the steerig column shaft by upper and lower plates 32,34 and the handle bars 35 are mounted on the upper plate 32. The girder fork tubes 24 are free to move up and down relative to the steering column 14 by virtue of the parallelogrammic linkage 28,30 under the control of resilient means in the form of one or more springs 36 extending generally diagonally across the parallelogram. In the illustrated embodiments, there is a single helically wound coil spring 36 whose upper end is connected to lower plate 34 by a U-shaped element 38 and whose lower end is connected to a crosspiece 39 between the tubes 24 by a U-shaped element 40.In this way, the coil spring 40 undergoes compression in response to upward movement of the front wheel and fork and the coil bound condition of the spring may act as a stop to limit the extent of such upwaard movement.

The two upper links 28 are rigidly connected together by a crosspiece 42 and the lower links 30 are likewise rigidly connected by a crosspiece 44 for the reason mentioned previously.

Each pair of links 28,30 and the associated crosspiece 42,44 form a component of H configuration. The driven rear wheel 46 of the cycle is driven in the usual way by a crank wheel, chain and gearing but in contrast to a conventional bicycle, the rear wheel is carried by a sub-frame comprising a pair of transversely spaced arms 48 whose forward ends are mounted at the bottom bracket 18 for pivotal movement in vertical planes about the spindle axis.

The rotational axis of the rear wheel is thereby maintained at a constant distance from the spindle axis so that chain tension remains constant during up and down movement of the rear wheel relative to the main frame.

Such up and down movement is controlled by a leaf spring set 50 whose lower end is rigidly secured to the main frame adjacent the bottom bracket 18.

The arms 48 are coupled to the upper free end of the leaf spring set 50 by transversely spaced arms 52 which are pivotally connected one to each of the arms 48 and to the leaf spring set. The leaf spring set 50 is of a preformed arcuate configuration which is outwardly convex with respect to the axis of the rear wheel 46. Thus, the sub-frame comprising arms 48 and 52 is biassed by the leaf spring set 50 to a predetermined position relative to the main frame and any up and down movement of the rear wheels results in stressing of the leaf spring set thereby cushioning such movement.

Claims (10)

1. A cycle frame comprising a main frame journalling a transverse shaft which forms an element in the drive transmission of the cycle, and a sub-frame which carries the driven wheel and which is pivoted on the axis of said shaft, resilient means being provided for urging said sub-frame to a predetermined range of positions relative to the main frame.

2. A cycle frame as claimed in Claim 1 in which said resilient means comprises at least one leaf spring having one end anchored to the main frame and the other end connected to said sub-frame such that the leaf spring biasses the sub-frame to a predetermined position or range of positions relative to the main frame and is stressed in response to pivoting of the sub-frame away from said predetermined position or positions.

3. A cycle frame as claimed in Claim 1 or Claim 2 in which said leaf spring is of preformed arcuate configuration.

4. A cycle frame as claimed in Claim 3 in which said leaf spring is outwardly convex with respect to the axis about which the driven wheel rotates.

5. A cycle frame as claimed in Claim 2 in which said sub-frame comprises a first pair of arms which aare pivoted on said shaft axis and carry the pivot wheel and a scond pair of arms which are pivotally connected one to each of said first pair of arms and to said other end of the leaf spring.

6. A cycle frame comprising girder forks mounting the front and steerable wheel, the girders being connected by means of parallelogrammic linkage to the steering column shaft, with spring means extending diagonally across the parallelogram to provide resilient suspension, characterised in that the links between the girder and column on one side of the fork are rigidly connected to the corresponding links on the other side of the fork.

7. A frame as claimed in Claim 6 in which the rigid connection between each pair of links is provided by a crosspiece in such a way that the links and crosspiece form a member of H configuration.

8. A frame as claimed in Claim 6 or 7 in which said resilient means comprises one or more general ly helica-, y or spirally wound springs extending generally diagonally across the parallelogram, with each end of each spring coupled to the parallelogram through the length of the spring so that when two points adjacent opposite ends of the spring move away from one another in suspension movement, the spring is shortened.

9. A cycle frame having the features claimed in any one of Claims 1 to 6 and any one of Claims 6 to 8.

10. A cycle frame substantially as hereinbefore described with reference, and as shown in, the accompanying drawings.