Technical Field

The present invention relates to a pre-load adjuster for a shock absorber for a vehicle, to a shock absorber comprising a pre-load adjuster and to a vehicle comprising a shock absorber.

Background to the Invention

Motorcycles and other vehicles are typically provided with suspension systems which are designed to maintain the wheels of the vehicle in contact with the ground. Many motorcycles employ a so-called monoshock rear shock absorber assembly having a fluid- filled cylinder in which a linearly moveable piston is received. A compression spring is disposed between a free end of the piston and a body of the cylinder to damp the motion of the piston. One end of the shock absorber assembly is linked to a body or frame of the motorcycle, whilst the other end is linked to a swingarm of the motorcycle, which carries the rear wheel.

The rear shock absorber assembly is designed partly to maintain the rear wheel in contact with the ground while the motorcycle is being ridden. For good handling characteristics it is important that the shock absorber does not reach the smallest limit of its compression. It is equally important that the shock absorber does not reach its furthest limit of extension. Both of these conditions can lead to poor handling characteristics.

To assist in preventing these conditions, and to compensate for different rider weights and riding styles, many rear shock absorbers are provided with pre-load adjusters. By adjusting the pre-load of the shock absorber (i.e. the degree of compression applied to the spring when no rider is present), the handling characteristics of the motorcycle can be tailored to individual rider weights and riding styles. Typically a pre-load adjuster comprises an internally threaded locking ring which engages with a thread provided on the body of the shock absorber and an internally threaded adjustment ring which engages with the thread of the shock absorber body and abuts an end of the compression spring. The adjustment ring can be rotated on the shock absorber body to vary the degree of compression of the compression spring, and the locking ring can be brought into engagement with the adjustment ring and locked to maintain the adjustment ring in position when a desired degree of compression (pre-load) has been achieved.

A disadvantage of known pre-load adjusters of this type is that the adjustment ring can be difficult to rotate, and a full 360 degree rotation of the adjustment ring on the thread is typically required before a noticeable difference to the handling characteristics of the motorcycle is achieved. Making adjustments to the pre-load of the shock absorber using such a pre-load adjuster is a time consuming and imprecise process.

Summary of Invention

According to a first aspect of the invention, there is provided a pre-load adjuster for a shock absorber, the pre-load adjuster comprising a first element which is engageable with a body of the shock absorber and a second element which is engageable with a spring of the shock absorber, the first element and the second element being movable relative to one another, the first element having a ramped formation having a plurality of spaced notches which are engageable with a protruding formation of the second element so as to adjust the spacing of the second element with respect to the first element.

The pre-load adjuster of the present invention overcomes the disadvantages of known pre-load adjusters by providing a mechanism which permits fast and accurate adjustment of the pre-load of a shock absorber.

Preferably, the first element can be locked in position on the body of the shock absorber. The first and second elements may be substantially annular.

An inner surface of the first element may comprise a thread which is engageable with a corresponding thread of the body of the shock absorber.

Advantageously, the spacing between the notches of the ramped formation is such that in moving the protruding formation of the second element from a position in which it engages with a notch to a position in which it engages with an adjacent notch the axial spacing between the first and second elements changes by a distance that is equal to the pitch of the thread of the body of the shock absorber.

This spacing between the notches of the second element permits a precise amount of preload to be imparted to the shock absorber in a single movement of the second element, thus simplifying the process of pre-load adjustment.

The first element may comprise three equally spaced ramped formations and the second body may comprise three equally spaced protruding formations.

The three equally spaced protruding formations provide stable and adequate support the first element, whilst also permitting an acceptably broad range of pre-load adjustment settings, as the ramped formations are long enough to include a number of notches, each of which corresponds to a discrete pre-load setting.

The first element may be coated in a friction-reducing material.

Similarly, the second element is coated in a friction-reducing material.

Coating the first and second elements with a friction-reducing element reduces friction between them, thus facilitating moving the second element with respect to the first, and movement of the first element with respect to the body of the shock absorber. The first element may comprise a unitary body.

The second element may comprise a unitary body.

The first element may comprise a bore which is able to receive a bar or rod to facilitate rotation of the first element around the body of the shock absorber.

The second element may comprise a bore which is able to receive a bar or rod to facilitate rotation of the second element around the body of the shock absorber.

The pre-load adjuster may further comprise a wear bush on which the second element can be mounted.

The wear bush is interposed between the body of the shock absorber and the second element when the pre-load adjuster is installed on the shock absorber, and acts to protect both the body of the shock absorber and the second element from damage caused by the second element bearing against the body of the shock absorber.

According to a second aspect of the invention there is provided a shock absorber comprising a pre-load adjuster according to the first aspect.

According to a third aspect of the invention there is provided a vehicle comprising a shock absorber assembly according to the second aspect.

Brief Description of the Drawings

Embodiments of the invention will now be described, strictly by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a perspective view of a part of a shock absorber comprising a pre-load adjuster according to an embodiment of the invention;

Figure 2 is a perspective view of a first element of a pre-load adjuster according to an embodiment of the invention;

Figure 3 is a cross-sectional view of the first element of Figure 2;

Figure 4 is a perspective view of a second element of a pre-load adjuster according to an embodiment of the invention;

Figure 5 is a cross-sectional view of the second element of Figure 4;

Figure 6 is a perspective view of a wear bush of a pre-load adjuster according to an embodiment of the invention; and

Figure 7 is a cross-sectional view of the wear bush of Figure 6.

Description of the Embodiments

Referring first to Figure 1 , part of a shock absorber assembly for the rear wheel of a motorcycle is shown generally at 10. The shock absorber assembly 10 comprises a number of components, but only those that are relevant to the present invention will be described here.

The shock absorber assembly 10 comprises a piston 12 which is received within a cylinder (not shown) and arranged for linear movement with the cylinder. A compression spring 14 is positioned co-axially around the piston 12, with one end abutting a shoulder of the cylinder and the other end abutting a pre-load adjuster 16. Thus, when the piston 12 is compressed, for example when a motorcycle on which the shock absorber assembly 10 is installed passes over a bump in the ground, the compression spring 14 is also compressed, thereby damping the movement of the piston 12.

The pre-load adjuster 16 comprises a lockable first element, which in this example is a first ring 18 having an internal thread which engages with an external thread 20 of the piston 12 to permit the position of the first ring 18 on the piston 12 top be adjusted. A second element of the pre-load adjuster 16, which in this example is a moveable ring 22, is mounted on a wear bush (not visible in Figure 1), a shoulder of which abuts the compression spring 14. The second ring 22 is moveable relative to the first ring 18 to adjust the axial spacing between the first ring 18 and the second ring 22, as is explained in detail below. Increasing the axial spacing between the first ring 18 and the second ring 22 increases the degree of compression of the compression spring 14, whilst reducing the axial spacing between the first ring 18 and the second ring 22 reduces the degree of compression of the compression spring 14. Thus, the pre-load of the shock absorber assembly 10 can be adjusted.

Figure 2 is a perspective view of the lockable first ring 18 of the pre-load adjuster 16. The first ring 18 comprises a unitary, substantially annular, body 30 formed of a metal such as aluminium or steel which may be coated with a friction-reducing material such as polytetrafluoroethene (PTFE) to reduce friction between the first ring 18 and the second ring 22, and between the first ring 18 and the piston 12 on which it is mounted, to facilitate installation and adjustment of the pre-load adjuster 16 on the piston 12. In this example the body 30 does not form a closed ring, but a small gap 32 is provided between ends 34, 36 of the body 30, to facilitate installation of the first ring 18 on the piston 12. It will be appreciated, however, that the body 30 of the first ring 18 may equally be formed as a closed ring.

The first ring 18 has a locking mechanism, which may comprise, for example, a threaded bolt which passes through a hole 48 positioned towards the free end 34 of the body 30 and engages with a correspondingly threaded bore provided in the free end 36 of the body to close the body 30 around the piston 12. This is merely one example of a suitable locking mechanism, and it will be apparent to those skilled in the art that other locking mechanisms are equally suitable.

An inner surface 38 of the body 30 has a thread (although this is not shown in Figure 2 for the purpose of clarity) which corresponds to the external thread 20 of the piston 12 of the shock absorber assembly 10, permitting the first ring 18 to be engaged with the piston 12.

The first ring 18 is provided with a plurality of bores or blind holes 40 around its circumference, into which a bar or rod can be inserted to facilitate rotation of the first ring 18 on the piston 12 to adjust the position of the first ring 18.

The first ring 18 is formed with a skirt 42 which extends axially from a surface of the body 30. The skirt 42 extends around the circumference of the body 30, and forms a plurality (in this example three) of ramped cam following surfaces 44, which can be seen more clearly in the cross-sectional view of Figure 3. The ramped cam following surfaces 44 are equally spaced around the circumference of the body 30. Thus in this example, where three ramped cam following surfaces 44 are provided, the ramped cam following surfaces 44 are provided at 120 degree intervals around the circumference of the body 30.

Each of the ramped cam following surfaces 44 is provided with a plurality of notches 46 which are configured to receive a protruding cam of the second ring 22. The notches 46 are equally spaced along the length of the ramped cam following surfaces 44, and provide a plurality of discrete settings for the pre-load of the shock absorber assembly 10, as will be explained below.

Figure 4 is a perspective view of the second ring 22, whilst Figure 5 is a cross-sectional view of the second ring 22. The second ring 22 comprises a unitary, substantially annular body 50 of a metal such as steel or aluminium, which may be coated with a friction- reducing material such as PTFE to reduce friction between the second ring 22 and the first ring 18.

The body 50 is provided with a plurality of bores or blind holes 52 around its circumference, into which a bar or rod can be inserted to facilitate rotation of the second ring 22 when it is mounted on the piston 12 of the shock absorber assembly 10.

A plurality (in this example 3) of projecting cams 54 extend axially from a surface of the body 50. The projecting cams 54 have rounded heads to facilitate their engagement with and disengagement from the notches 46 of the ramped cam following surfaces 44 of the first ring 18. The projecting cams 54 are equally spaced around the circumference of the body 50. Thus, in the example shown in Figure 4 the projecting cams are spaced at 120 degree intervals around the circumference of the body 50.

When the shock absorber assembly 10 is assembled, the second ring 22 is mounted on a wear bush, which is shown generally at 60 in Figures 6 and 7. The wear bush 60 is made from a low-friction material such as polyoxymethylene (which is marketed under the trade mark Delrin ®) and comprises a generally annular first part 62, whose outer diameter is slightly smaller than an inner diameter of the second ring 22, and a generally annular second part 64, whose outer diameter is slightly smaller than an inner diameter of the spring 14 of the shock absorber assembly 10. Disposed between the first part 62 and the second part 64 is an annular shoulder 66 whose outer diameter is substantially equal to an outer diameter of the spring 14.

Thus, when the shock absorber assembly 10 is assembled, one end of the compression spring 14 abuts the cylinder, whilst the other end of the compression spring 14 receives the second part 64 of the wear bush 60 and abuts a first surface 68 of the shoulder 66. The second ring 22 is mounted co-axially with the wear bush 60, over the first part 62 of the wear bush 60 such that it rests on a second surface 70 of the shoulder 66. In the example shown in Figure 1, the protruding cams 54 of the second ring 22 extend in a generally upward direction when the shock absorber assembly 10 is assembled.

The first ring 18 engages with the piston 12 by means of the engagement between the external thread 20 of the piston 12 and the thread provided on the internal surface 38 of the first ring 18. In the example shown in Figure 1, the skirt 46 extends in a generally downward direction. The first ring 18 can be locked in a desired position by means of the locking mechanism.

The second ring 22 is biased towards the first ring 18 by the compression spring 14, and is maintained in an axially spaced relationship with the first ring 18 by the protruding cams 54, which are each received in a notch 46 of one of the ramped cam following surfaces 44 of the first ring 18. In this example the first ring 18 has three equally spaced, similar ramped cam following surfaces 44 and the second ring 22 has three equally spaced, similar protruding cams 54. The applicants have found that this arrangement provides stability, as the three equally- spaced similar protruding cams 54 support the first ring 18, whilst also permitting a reasonable range of discrete pre-load settings. Nevertheless, more than three protruding cams 54 and ramped cam following formations 44 could be employed in a pre-load adjuster 16.

The axial spacing between the first ring 18 and the second ring 22 can be adjusted by rotating the second ring 22 about the piston 12 such that the protruding cams 54 are received in different notches 46 of the ramped cam following surfaces 44 of the first ring. Thus, to increase the axial spacing between the first ring 18 and the second ring 22, the second ring 22 is rotated to bring the protruding cams 54 into engagement with notches 46 which are located a greater distance along the ramped cam following surfaces 44 of the first ring 18 (i.e. are located at a greater axial distance from the body 30 of the first ring 18). To reduce the axial spacing between the first ring 18 and the second ring 22, the second ring 22 is rotated in the opposite direction to bring the protruding cams 54 into engagement with notches 46 which are located a smaller distance along the ramped cam following surfaces 44 (i.e. are located at a smaller axial distance from the body 30 of the first ring 18).

By adjusting the axial spacing of the moveable second ring 22 with respect to the lockable first ring 18 in this way, the degree of compression of the compression spring 14 can be adjusted.

In the example illustrated in Figures 1 - 7, the pre-load adjuster 16 is configured to provide four discrete pre-load settings, as four notches 46 are provided in each of the ramped cam following formations 44. However, more or fewer notches 46 may be provided, to increase or decrease the number of discrete pre-load settings permitted by the pre-load adjuster 16.

In this example, the distance between the notches 46 of the ramped cam following formations 44 is selected such that in rotating the second ring 22 from a position in which the protruding cams are received by one set of notches 46 to a position in which the protruding cams 54 are received by an adjacent set of notches 46 the difference in the axial spacing between the first ring 18 and the second ring 22 corresponds to that which would be achieved by rotating the first ring 18 through 360 degrees around the piston 12 (i.e. the pitch of the thread 20). In this example the pitch of the thread 20 is approximately 1.5mm, so rotating the second ring 22 by one notch 46 corresponds to a change of approximately 1.5mm in the axial spacing between the first ring 18 and the second ring 22, and thus to a change of 1.5mm in the length of the compression spring 14 and a corresponding change to the pre-load of the shock absorber assembly 10.

In the event that a greater or lesser degree of pre-load is desired, the first ring 18 can be unlocked from the cylinder 12 and repositioned by rotating it in an appropriate direction to increase or decrease the axial distance between the first ring 18 and the cylinder, thus adjusting the length of the compression spring 14 prior to any additional adjustment being applied by the pre-load adjuster 16. Although the pre-load adjuster 16 has been described in the context of a shock absorber assembly 10 for a motorcycle, it will be appreciated that the pre-load adjuster is equally suitable for other applications, such as a shock absorber for a rally car, race car, trials, motocross, or enduro motorcycle or quad bike.