GB2154960A

GB2154960A - An improved motorcycle front fork assembly

Info

Publication number: GB2154960A
Application number: GB08405606A
Authority: GB
Inventors: Terence Anthony Haynes
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-09-17
Filing date: 1984-03-02
Publication date: 1985-09-18
Also published as: GB8405606D0; WO1987001670A1; GB2154960B; EP0236303A1

Abstract

A motorcycle front fork assembly incorporates in each leg telescopic elements (19) and a pivoted wheel supporting lever (17). A single suspension unit (28) is pivotally mounted on the frame (33) of the motorcycle with the connection between the telescopic elements (19) of the articulated mechanism and the suspension unit (28) being via a bridge piece (29) which unites the upper ends of the telescopic elements (19) where they protrude from their respective housings (30) mounted within the fork legs (15), and which carries in its centre a universal joint (31) arranged to lie on the steering axis (C1) of the motorcycle. A link (26) is pivotally connected to the universal joint with a restraining link (27) pivotally connected to the frame (33) and pivotally connected to the lower end (34) of the suspension unit (28). <IMAGE>

Description

SPECIFICATION An improved motorcycle front fork assembly From U.K. application 8221493, PCT GB83/00179 a motorcycle fork asembly is known as illustrated fig. 1 comprising substantially parallel fork legs (15) each leg being connected to an articulated linkage (16). The articulated linkage comprises a telescopic member (19) concentric with or adjacent to each fork leg (15) and axially movable substantially in the plane of the fork legs and a suspension link (17) having a first end for supporting the wheel spindle (24), a second end (22), and being pivotally connected between the two ends (22,24) to the telescopic member (19).Restraining means in the form of a link (18) or alternatively other means such as a roller and track allow translational movement of the second end (22) of the suspension link (17) during axial movement of the telescopic member (19) in response to movement of the said first end.

An object of this present invention is to minimise the inertia of the front fork in the side-to-side 'steering' mode, whereby this object can be achieved by arranging for the resilient means of suspension to be by a single suspension unit housed within, or bolted to the frame or chassis of the motorcycle, and operating on the suspension means via a universal joint and linkage so that steering and suspension movement are separated, and the mass of the suspension means is removed from the side-to-side steering movement of the fork.

A further object of the present invention is to arrange that this linkage operates in such a manner as to provide initially very compliant suspension characteristics that become progressively firmer with wheel excursion.

A further object of the invention is to minimise the effective 'unstrung inertia of the moving parts, and provide a convenient mounting point for the mudguard.

A further object is to unite the articulated mechanisms in each leg so as to ensure that they operate simultaneously to prevent or obviate any twisting or bending of the wheel spindle and consequent misalignment.

Fig 2 illustrates the essential characteristics of the present invention.

Fig 3 shows in elevation and section an embodiment of the present invention in which a single suspension unit provides the resilient means of suspension.

Fig 4a through to 4e shows alternative constructions in which the suspension means are located in similar ways to achieve the objects of the present invention.

Fig.5 illustrates diagramaticaly the movement of the telescopic elements (19), main link (26), restraining link (27) and suspension unit (28), at various points of wheel movement as plotted at the wheel spindle (24).

Fig.6 is a graph where the compression of the suspension unit (x axis) is plotted against the wheel travel (y axis).

In fig.2 a fork assembly is shown comprising an articulated mechanism in the base of each leg as according to U.K. 8221493 a link (17), a telescopic element (19), and restraining means by a link (18).

It is a characteristic feature of the present invention that the telescopic elements are arranged to work in the same plane as the steering axis. Further that the telescopic elements are disposed so that the steering axis bisects a horizontal line drawn between the telescopic elements, or that such a line is only displaced laterally from the steering axis by a small amount, as may be accomodated by the bridge piece (29).

According to the present invention the telescopic elements are carried in housings or linear bearings mounted within the fork legs.

The housings or bearings (30) are open at their upper ends so that the top of the telescopic elements may project through. A rigid bridge piece (29) is bolted, clamped, splined or otherwise firmly mounted to the tops of the telescopic elements so as to unite them. The fork structure is relieved locally or pierced to provide axial working clearance for the bridge piece. In the centre of the bridge piece, and arranged to lie exactly under the steering axis, is provided a universal joint (31), which connects with a linkage mechanism. In the embodiment in fig.3 this mechanism comprises a main link (26), a restraining link (27), acting upon a suspension unit (28).

The suspension means is shown as a conventional coil spring/hydraulic damper unit, but other suspension means may be employed such as may be provided by the compression of a gas or rubber compound.

The upper end (32) of the suspension unit (28) is pivotally mounted on a convenient bracket to the motorcycle frame (33), whilst the lower end (34) bears aproximately midway along the link (26).

In operation movement of the wheel as plotted at the wheel spindle (25) produces a corresponding axial motion of the telescopic elements (19). The bridge piece is thus caused to move in the plane of the steering axis, and by virtue of the universal joint (31) and links (26,27) compresses the suspension unit.

By arranging for the steering axis to pass exactly through the universal joint centre, any movement of the fork side-to-side has no effect on the suspension unit. Similarly, up and down movement of the bridge piece and corresponding compression of the suspension unit has no effect on the action of the fork side-to-side.

Fig. 5 shows the movement of the wheel at the wheel spindle (24) as it follows the path (25), and the corresponding motion at the lower end of the suspension unit (34). The wheel spindle is plotted at equal 20m/m steps over a total length of 160m/m, and it will be apparent that for a wheel travel of 160m/m, the suspension unit is compressed by only 72 m/m. Thus the effective inertia of the suspension unit is reduced by the ratio of these travels, ie by 55%. Similarly the bridge piece only moves a total of 105m/m, so utilising this as a mounting point for a mudguard effectively reduces the inertia of this component by 34 %, compared with the normal method of mounting mudguards by brackets or stays to a point close to or on the wheel spindle.

Fig 6 illustrates by means of a graph a further feature of the linkage mechanism. As can be seen, the line (R1) plotting wheel travel against suspension means compression, is curved, so that compression of the suspension means at the beginning of wheel travel is comparatively less than at subsequent points.

Alterations to the geometry of the linkage, specifically changes in the shape of the link to a bell-crank lever may enhance or reduce this effect.

Changes in the disposition, length and mounting position of the restraining link (27) also influence this rising-rate effect, which is known to improve the over-all compliance of the suspension system.

Fig. 3 illustrates a typical bridge piece, the principal characterising features being the rigid construction enabling it to transmit the suspension loads and prevent axial misalignment of the telescopic elements.

Claims

1. A motorcycle front fork assembly incorporating in each leg an articulated mechanism as known from U.K. 8221493 and PCT GB83/00179, arranged so that the telescopic elements (19) operate axially in the plane of the steering axis of the motorcycle; resilient means of suspension provided by a single suspension unit (28) pivotally mounted on the frame (33) of the motorcycle; the connection between the telescopic elements of the articulated mechanism and the suspension unit being via a bridge piece (29) uniting the upper ends of the telescopic elements where they protude from their respective housings (30) mounted within the fork legs (1 5); the fork legs being so shaped, relieved or pierced locally as to provide working clearance for the axial movement of the bridge piece; this bridge piece carrying in its centre a universal joint (31) arranged to lie on the steering axis (C1) of the motorcycle; and a link (26) is pivotally connected to the universal joint with a restraining means (27), pivotally connected to the frame (33) allowing translational movement of the link with axial movement of the bridge piece (29), and pivotally connected to the lower end (34) of the suspension unit (28), so that movement of the wheel as plotted at the wheel spindle (24) is conveyed via the universal joint (31) in the centre of the bridge piece directly under the steering axis (C1) to the link (26) which acts upon the suspension means (28).

2. A motorcycle front fork assembly incorporating in each leg an articulated mechanism as known from U.K. 8221493, arranged so that the telescopic elements (19) operate in the plane of the steering axis of the motorcycle; resilient means of suspension being provided by a single suspension unit (28) pivotally mounted on the frame (33) of the motorcycle; the connection between the telescopic elements (19) of the articulated mechanism and the suspension unit being via a bridge piece (29) uniting the upper ends of the telescopic elements where they protrude from their respective housings (30) mounted within the fork legs (15); the fork legs being so shaped relieved or pierced locally as to provide working clearance for the axial movement of the bridge piece; this bridge piece carrying in its centre a universal joint (31) arranged to lie on the steering axis (C1) of the motorcycle; and a link (26) is pivotally connected from a point (35) on the motorcycle frame, and connected to the universal joint via a link (36) at point (37) to allow for the difference in motion between the axial movement of the bridge piece, and the arcuate movement of the link (26). And a point (34) on the link (26) carries a lower pivotal mounting for the suspension means so that motion of the bridge piece as induced by wheel travel is conveyed via the universal joint (31) and link (36) to operate on the link (26) and thus act upon the suspension means.

3. A motorcycle front fork assembly as claims 1 and 2 wherein the bridge piece (29) is rigidly fixed to the top ends of the telescopic elements (19) so as to unite them and whereby the construction of the bridge and method of fixing eliminates or minimises any differential axial displacement of the telescopic elements.

4. A motorcycle front fork assembly according to claim I wherein the link (26) is connected pivotally at its foward end to the universal joint (31), and a restraining means comprising a link (27) pivotally connected between the second end (38) and a point on the motorcycle frame (35) allowing translational motion of the link (26) with axial motion of the bridge piece (29), and a suspension means (28) is provided pivotally mounted at its upper end to a point (32) on the motorcycle frame (33) behind the steering axis (C1) and at its lower end pivotally mounted between the points (31) and (38).

5. A motorcycle front fork assembly according to claim 1 wherein the link (26) is ex tended forward of the universal joint (31), and a suspension means (28) pivotally mounted at its upper end to a point (32) on the motorcycle frame forward of the steering axis (C1), and at its lower end (34) pivotally connected to the foward extremity of the link (26); and a restraining means comprising a link (27) pivotally connected between the second end (38) and a point on the motorcycle frame (35) allowing translational motion of the link (26) with axial motion of the bridge piece (29).

6. A motorcycle front fork assembly according to claim 1 wherein the restraining means (27) allowing translational motion of the link (26) is pivotally connected between a foward extension of the link (26) and a point on the frame (35) forward of the steering axis, and the suspension means (28) is pivotally connected at its upper end to a point (32) on the motorcycle frame behind the steering axis, and at its lower end (34) pivotally connected to the link (26) at its second end (38), with the universal joint being pivotally connected to a point (31) between the first and second ends of the link (26).

7. A motorcycle front fork assembly according to claim 2 wherein the link (26) is pivotally mounted from a point (35) on the motorcycle frame, and the suspension means (28) is mounted pivotally at its upper end on the frame behind the steering axis at point (32), and at its lower end connected pivotally to link (26) at a point (34) between points (35) and (37).

8. A motorcycle front fork assembly according to claim 2 wherein the link (26) is pivotally mounted from a point (35) on the motorcycle frame, and the suspension means (28) is mounted pivotally at its upper end on the frame in front of the steering axis at point (32), and at its lower end connected pivotally to link (26) at a point (34) in front of the steering axis, and link (36) pivotally connects the universal joint (31) to point (37) between points (34) and (35).

9. A motorcycle front fork assembly according to claim 2 wherein the link (26) is pivotally mounted from a point (35) on the motorcycle frame in front of the steering axis, and a suspension means (28) is mounted pivotally at its upper end on the frame behind the steering axis at point (32), and at its lower end connected pivotally to the second end of the link (26) at point (34), the link (26) being connected pivotally to the universal joint (31) by a link (36) at point (37) between points (35) and (34)

1 0. A motorcycle front fork assembly according to claims 1 and 2 wherein the bridge piece (29) forms an attachment point for a mudguard.

11. A motorcycle front fork assembly according to claims 1,2,4,5,6,7,8, and 9, whereby the shape and disposition of the links (26) and (27), and the respective mounting position of the suspension means produces a progressively increasing ratio of movement as measured at the wheel spindle (24) and the lower pivotal mounting point of the suspension means (34) such that initial movement of the wheel induces a small movement or compression of the suspension unit, and that this compression of the suspension unit becomes comparatively larger as wheel excursion continues.