GB2167361A

GB2167361A - Motor cycle rear wheel suspension

Info

Publication number: GB2167361A
Application number: GB08408547A
Authority: GB
Inventors: Andrew Ford
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-04-03
Filing date: 1984-04-03
Publication date: 1986-05-29
Also published as: GB8408547D0

Abstract

A motor cycle has a rear suspension system comprising a swing arm assembly (5) which carries the rear wheel axle at its rearward end, and a compensating link (9) horizontally pivoted at its respective ends (C, E) to the front end of the swing arm assembly (5) and to the main motor cycle frame (1) rearwardly of the axis of a chain drive sprocket (8). A rocker lever (10) is located above the compensating link (9) and is horizontally pivoted (H) between its ends upon the main frame (1). Spring means (11) acts between the front end of the rocker lever (10) and a point (L) on the frame (1), and a first coupling rod (12) pivotally interconnects the front end of the swing arm assembly (5) with the rear end of the rocker lever (10). A second coupling rod (13) pivotally interconnects the compensating link (9) with the rocker lever (10) at a point (G) intermediate the pivotal connection of the rocker lever (10) to the main frame (1) and the first coupling rod (12). The relative lengths and points of pivotal connection (B,F,D,G) of the first (12) and second (13) coupling rods to the swing arm assembly (5), the compensating link (9) and the rocker lever (10) are such that any angular movement of the swing arm assembly (5) caused by force applied to the rear end thereof causes a relative angular movement of the compensating link (9) which is sufficient to ensure that the distance between the rear wheel axle (A) and the axis of the driving sprocket (8) remains constant. This ensures a constant chain tension. <IMAGE>

Description

SPECIFICATION Motor cycle rear wheel suspension system This invention relates to a rear wheel suspension system for chain-driven motor cycles.

In virtually all known chain-driven motor cycles it is common practice to mount the rear wheel axle between the rear end parts of a swing arm assembly which at its front end is horizontally pivotally attached to the main frame of the machine, the vertical movement of the assembly in relation to the frame being controlled by spring and shock absorbing means. Because the pivot axis, for design reasons, cannot coincide with the axis of the engine drive sprocket but is located rearwardly thereof, various, often complicated, expedients have hitherto been adopted or proposed for ensuring that there is a constant driving chain tension irrespective of the angular position of the swing arm assembly relative to the main frame when the motor cycle is in motion.This is of particular importance in high performance motor cycles which have to transverse rough ground and wherein the amplitude of angular movement of the swing arm assembly has to be considerable.

The present invention has been devised with the aim of providing a particularly simple and reliable rear wheel suspension system for maintaining a constant separation distance between the axis of the chain driving sprocket and the rear wheel or chain driven sprocket, thus maintaining constant chain tension.

There is thus proposed in accordance with the invention a motor cycle having a rear suspension system comprising a swing arm assembly carrying the rear wheel axle at its rearward end, a compensating link horizontally pivoted at its respective ends to the front end of the swing arm assembly and to the main motor cycle frame rearwardly of the axis of a chain drive sprocket, a rocker lever located above the compensating link and horizontally pivoted between its ends upon the main frame, spring means acting between the front end of the rocker lever and a point on the frame, a first coupling rod which pivotally interconnects the front end of the swing arm assembly with the rear end of the rocker lever and a second coupling rod which pivotally interconnects the compensating link with the rocker lever at a point intermediate the pivotal connection of the rocker level to the main frame and the first coupling rod, the relative lengths and points of pivotal connection of the first and second coupling rods to the swing arm assembly, the compensating link and the rocker lever being such that any angular movement of the swing arm assembly caused by force applied to the rear end thereof causes a relative angular movement of the compensating link which is sufficient to ensure that the distance beween the rear wheel axle and the axis of the driving sprocket remains constant.

The invention is hereafter described in more detail by reference to the accompanying somewhat simplified drawings. In these drawings Fig. 1 is a right side elevation of the rear suspension system and Fig. 2 is a plan view.

Referring mainly to Fig. 1 there is shown the position of some motor cycle main frame parts 1, engine and gearbox 2 and rear wheel 3. The rear wheel axle 4 is supported in generally known fashion between the rearward ends of a pair of parallel swing arms or swing arm assembly 5. Also shown is a sprocket 6 fixed to the wheel 3 and rotatable by the chain 7 from the driving sprocket 8.

The front end of the swing arm assembly 5 is indirectly connected to the frame 1 by an intervening compensating link 9 which is pivotally connected to the swing arm at C and pivotally connected to the frame 1 at E.

Above these components there is a rocker lever 10 which is pivotally attached to the main frame at H. The front end K of the lever 10 is adapted to engage the upper end of a coil spring 11 which surrounds an internal guide and is supported at the bottom upon a fixed frame projection L.

The rear end of the rocker lever 10 is pivotally connected at F to the upper end of a first coupling rod 12 which has its lower end pivotally connected at B to the swing arm 5.

Additionally the rocker lever 10 is pivotally connected at G, between the pivot points F and H, to the upper end of a second coupling rod 13 which has its lower end pivotally connected to the compensating link 9 at a point D-between the pivot points C and E.

The mode of operation of the suspension system is as follows.

When the wheel 3 encounters a bump, the swing arm 5 turns in a clockwise direction and, by action of the first coupling rod 12, causes the rocker lever 10 to swivel about the pivot point H so that the front end K of the lever 10 compresses the spring 11 which damps the movement. Simultaneously the second coupling rod 13 is drawn upwardly and causes the compensating link to turn clockwise through a small angle about the fixed pivot E. In so doing, by action of the pivotal connection C, it slightly raises the front end of the swing arm 5. The result of these movements is that during the whole of the upward swinging movement of the swing arm 5, the rectilinear distance between the wheel axis A and the drive sprocket axis S has been maintained constant. As a consequence there is no slackening or tightening of the chain 7.

The same effect is achieved by reverse action of the suspension components if the wheel 3 encounters a depression in the terrain which is being traversed. in the embodiment described, when the axle 4 moves upwards along an arc about pivot point E, the pivot point F moves upwards and pivot point G moves upwards to cause the point D to be pulled upwards. It should be noted that points A, C, E and S should be in a straight line when the wheel 3 is at the mid-point of its arcuate travel.

The attainment of the foregoing results is of course dependent upon the correct geometry of the various componets of the system, that is to say the selection of suitable length components and careful selection and adjustment of the points of pivotal connection. In general these will need to be varied to suit differently designed motor cycles using empirical methods or trial and error. Thus the pivotal point D can be anywhere between the pivotal points C and E and preferably somewhat above the pivotal point C so that no upward force is applied at E. The pivotal point G can be anywhere along the rocker lever 10 between the pivotal points F and H. The pivotal point L may be attached either to the frame 1, as shown, or to a point on the compensating link 9 between the pivotal points E and the pivotal point C preferably adjacent or above the point E. However this may cause too much strain on points E and C and as the point C moves upwards only very slightly in relation to the axis A, to have the spring thus attached could cause it to be simultaneously compressed from both ends. In fact point L can be anywhere upon the machine; the position of point L is not relevant.

Claims

1. A motor cycle having a rear suspension system characterised in that a swing arm assembly which carries the rear wheel axis at its rearward end, has its front end pivotally connected to the rear end of a link which at its front end is pivotally connected to the motor cycle frame.

2. A motor cycle having a rear suspension system comprising a swing arm assembly carrying the rear wheel axle at its rearward end, a compensating link horizontally pivoted at its respective ends to the front end of the swing arm assembly and to the main motor cycle frame rearwardly of the axis of a chain drive sprocket, a rocker lever located above the compensating link and horizontally pivoted between its ends upon the main frame, spring means acting between the front end of the rocker lever and a point on the frame, a first coupling rod which pivotally interconnects the front end of the swing arm assembly with the rear end of the rocker lever and a second coupling rod which pivotally interconnects the compensating link with the rocker lever at a point intermediate the pivotal connection of the rocker lever to the main frame and the first coupling rod, the relative lengths and points of pivotal connection of the first and second coupling rods to the swing arm, the compensating link and the rocket lever being such that any angular movement of the swing arm caused by force applied to the rear end thereof causes a relative angular movement of the compensating link which is sufficient to ensure that the separation distance between the axis of the chain driving sprocket and the rear wheel or chain driving sprocket is always constant, thus maintaining constant chain tension.

3. A motor cycle rear suspension system constructed substantially as hereinbefore described with reference to the accompanying drawings.

1. A motor cycle having a rear suspension system characterised in that a swing arm assembly which carries the rear wheel axle at its rearward end, has its front end directly pivotally connected to the rear end of a single link which at its front end is directly pivotally connected to the motor cycle frame.