This invention relates to a motorcycle frame and a motorcycle incorporating it.

A motorcycle frame or chassis is the base on which other components of the motorcycle including handlebars, fuel tank, seat, swing arm, shock absorber(s) and wheels are mounted. A number of motorcycle frame or chassis types are available for use. A monocoque frame forms an integral part of the body of the motorcycle. An alternative frame type has a trellis or lattice structure. A trellis or lattice structure, as its name suggests, comprises a lattice of tubes which have stiffness or rigidity balanced to provide a motorcycle rider with desired handling characteristics. In a motorcycle, excess stiffness or rigidity diminishes handling but the same is also true if stiffness or rigidity is insufficient. In this latter case, the flexing and deformation of the frame - particularly during cornering - will result in poor handling characteristics with a rider forced to compensate for the handling imperfection by other means either through postural movement or reducing engine power output which is clearly undesirable in racing type applications. Reading of motorcycle reviews readily supports the importance of handling.

Trellis frames have, so far, been used in relatively small volume production, most notably for racing type motorcycles. Ducati is one prominent manufacturer of motorcycles with trellis type frames. KTM Sportmotorcycle is another.

US Patent Application No. 2008/0060865, assigned to KTM Sportmotorcycle AG, discloses a motorcycle frame having tubes extending away from a steering head tube in a three dimensional trellis composite assembly of frame main tubes, interconnected by frame struts, paired upper and lower frame main tubes oriented, along at least a portion of their lengths, substantially parallel to each other. A single tube is oriented parallel to the lower frame main tubes, and arranged between the upper frame main tubes and the steering head tube.

US Patent No. 5480001, assigned to Honda Motor Co Ltd, discloses a frame structure for a motorcycle or the like wherein the swing arm is pivotably supported at its front end to a rear portion of a body frame. A single main pipe is a component of the body frame composed of a rearwardly extending portion located over an engine and extending rearwardly from a head pipe. A bent portion extends from a rear end of the rearwardly extending portion. A downwardly extending portion extends downwardly from the bent portion. A pair of cross pipes extends laterally with the cross pipes vertically spaced from each other being connected at their intermediate portions to the downwardly extending portion. A pair of supporting plates or gussets is located on the left and right sides of the downwardly extending portion being connected to both ends of the cross pipes. A swing arm is pivotably supported at its front end to a pivot shaft located between the cross pipes and extends between the supporting plates.

However, in a trellis type frame, the engine is a fully stressed member mounted to the main frame. As such, the engine is acted on by shock forces arising whilst the motorcycle is in operation. It would be desirable to reduce the magnitude of such shock forces acting on the engine, particularly in the case of smaller engines.

With this object in view, the present invention provides a motorcycle frame comprising a lattice of tubes extending rearward from a steering head mounting tube, the lattice including a main frame comprising main frame tubes, rear frame tubes and frame struts linking the main frame tubes wherein at least one additional tube is provided to extend in a direction between the rear frame tubes and the steering head mounting tube. Such a frame configuration allows load carrying by tubes other than the main frame tubes, which also act as engine mounting members, so reducing stresses in the main frame engine mounting members during operation of a motorcycle incorporating the frame.

Advantageously, the main frame tubes form a main frame structure, advantageously of open construction to facilitate mounting of components and minimize weight and frame material costs, comprising paired upper and lower main frame tubes oriented, along at least portion of their lengths, substantially parallel to each other. The upper main frame tubes advantageously have larger cross sectional area than the lower main frame tubes. The at least one additional tube advantageously comprises a pair of additional tubes, each additional tube being connected, either directly or indirectly, to at least one of the upper main frame tubes. Conveniently, in one embodiment, each additional tube is connected to a cross tube extending between the upper main frame tubes. In such case, each additional tube may be connected to a corresponding end of the cross tube. The cross tube may be gusseted to at least one of the upper main frame tubes to impart greater rigidity and better absorption of shock forces. The area and thickness of the gussets may be dictated by the desired stiffness of the frame.

Forward portions of the main frame upper tubes converge in the direction of the steering head mounting tube. Similarly, forward portions of the main frame lower tubes converge in the direction of the steering head mounting tube. The angle of the aperture between the converging upper and lower main frame tubes may also be dictated by, i.e be a function of, the rigidity required of the frame structure as well as the dimension and shape of engine and other components, such as fuel tank, to be mounted by the main frame.

The inclusion of the additional tube(s) results in a distribution of force, translated into the rear frame tubes, in the region of the shock absorber -swing arm mounting (which may be referred to as the shock pivot), to the additional tubes and on to the cross tube such that the main frame is substantially released or discharged from shock forces during operation of a motorcycle incorporating the frame. To this end, the additional tube(s) may form a direct or a nearly direct joint from the shock absorber-swing arm mounting tube to the steering head mounting tube. That is, shock forces - or a majority of the shock forces translated from the swing arm and a rear shock absorber of a motorcycle incorporating the frame - to the frame is directed along the additional tube(s), to the cross tube and steering head mounting tube, and not significantly into the lattice structure of the main frame.

The additional tube(s) need not span the whole distance between the shock pivot and the steering head mounting tube though maximum release of the main frame from shock forces may be achieved if this is the case. The additional tube(s) may span less than this distance. Packaging constraints, as well as the object of optimising use of material, may require that the span be reduced in such a manner.

The frame structure is triangulated to provide stiffness and rigidity whilst saving on the amount of material used to fabricate the frame. At the same time, the constituent tubes of the frame are subject to low bending stresses. Struts and main frame tubes may be welded to each other. Robotic welding allows for precision welding and adaptability to mass production. If desired, welds may be laser trimmed to ensure the desired quality.

When the engine is mounted to the main frame, with the assistance of the frame struts and/or mounting means (such as mounting plates) connected to the frame struts, the engine forms a stressed member, typically a fully stressed member, of the frame. The engine can thus be used to assist in stiffening the frame. However, unlike previous trellis type frames, the release or discharge of the main frame from shock forces during operation, such as on road riding, of the motorcycle results in a reduced shock forces acting on the engine.

The frame of the present invention, being comprised of a relatively low number of tubes, is well applied to faster fabrication. The frame also advantageously incorporates forged components to further facilitate time efficient mass production. Forged components may include the shock mounting and the steering head tube as well as joints in the frame. For example, the swing arm pivot mounting, and the footpeg/pedal mounting may be a forged component as may the upper shock absorber mounting on the frame.

The swing arm pivot and footpeg/pedal mountings each have respective portions on each side of the frame correspondent with right and left hand sides of a motorcycle. These portions, which are conveniently of sheet metal, will be termed the right and left side swing arm pivot portions in this specification. In order to reduce assembly stresses when the swing arm is clamped to the frame, a stiffening tube is disposed, and joined to the portions, between the swing arm pivot portions.

While the frame is comprised of tubes, these need not be of circular cross section. An elliptical or oval section for the frame tubes may advantageously be employed. Alternative shapes, such as polygonal shape, may also be employed.

In a further aspect, the present invention provides a motorcycle incorporating a frame as above described.

The motorcycle frame has a high degree of rigidity in the vertical, frontal and lateral directions while minimising the weight of the frame. At the same time, the engine - when mounted to the main frame - is subject to a lower magnitude of shock forces arising during operation than previous frame designs. Further, the frame achieves these benefits whilst maintaining a slender appearance for a motorcycle with desirable handling characteristics.

The motorcycle frame of the present invention may be more fully understood from the following description of a preferred embodiment of the frame which is made with reference to the accompanying figures in which:

Figure 1 is a top view of a motorcycle frame in accordance with a preferred embodiment of the present invention;

Figure 2 is a side view of the motorcycle frame shown in Figure 1;

Figure 3 is an isometric view of the motorcycle frame of Figures 1 and 2 and showing the rear shock absorber when mounted to the frame;

Figure 4 is an isometric view of the motorcycle frame of Figures 1 and 2 and showing a swing arm mounted to the frame;

Figure 5 is a detail rear view showing a pivot mounting for the swing arm as shown, generally, in Figure 4; and

Figure 6 is a detail side view showing the pivot mounting of Figure 4 and the connection between the front and rear portions of the frame;

Figure 7 is a front perspective view of the frame shown in Figures 1 to 4 showing connection of the frame to the front fork tubes; and

Figure 8 is a motorcycle incorporating the frame as shown in Figures 1 to 4;

Referring now to Figures 1 to 4, there is shown a motorcycle frame 10 comprising a lattice of tubes extending rearwardly away from a steering head mounting tube 15. The lattice, of open structure, includes a main frame 12 comprising main frame tubes 16, 17 and frame struts 18 linking these and rear frame tubes 35. At least one additional tube 30, additional to the main frame tubes 16, 17 and frame struts 18, is provided to extend between the rear frame tubes 35 and the steering head mounting tube 15 to absorb shock forces and so reduce shock forces acting on the main frame 12 during operation of a motorcycle incorporating the frame 10.

The main frame 12 comprises paired upper and lower main frame tubes 16, 17 oriented substantially parallel to each other along a substantial portion, though not the whole of their length, as will be described below. The main frame tubes 16 and 17 are joined to the steering head mounting tube 15 at their forward ends, for example by welding. Forward ends 16a of upper main frame tubes 16 converge towards each other, or put another way, extend away from the steering head mounting tube 15, defining an aperture angle 19. Similarly, forward ends 17a of the lower main frame tubes 17 converge towards each other, or put another way, extend away from the steering head mounting tube 15, also defining an aperture angle 19.

It will be noted that the upper tubes 16 have larger cross sectional area than the lower tubes 17. Accordingly, the upper tubes 16 have a greater rigidity or stiffness and resistance to bending.

Upper and lower main frame tubes 16 and 17 are interconnected by frame struts, in the form of tubes 18. The number of frame struts 18 is selected to impart the required rigidity or stiffness of the frame 10 for desired handling characteristics. The frame struts 18 are conveniently welded between the upper and lower main frame tubes 16 and 17. It may be observed that the frame struts 18 are so disposed between the upper and lower main frame tubes 16 and 17 as to form a triangulated structure. It may also be observed that the frame struts 18 are not connected to the steering head tube 15.

Upper and lower main frame tubes 16 and 17 are fitted with mounting brackets 43 for mounting of the engine and other components of a motorcycle to the main frame 12. The engine 72, illustrated in Fig. 8, may be a four stroke cycle engine though other engine types are not precluded. The frame 10 may be connected to front fork tubes 110 at two spaced mounting points 150 and 152 spaced at opposed ends of the steering head mounting tube 15 as shown in Figure 7. Rearwardly of the rear frame tubes 35 are connected rear frame extension tubes 37 which are used to mount the seat of a motorcycle as well as the tail light assembly.

The upper main frame tubes 16 are connected by a cross tube 50 which extends transversely to an axis of motorcycle frame 10. Cross tube 50 is located towards the front portion of the frame 10 and it may be located at the point from which the upper main frame tubes 16 start to converge as described above. There is no necessity for a similar cross tube to be mounted between the lower main frame tube members 17. The role of cross tube 50 will be described further below.

A pair of additional tubes 30, of approximately the same diameter as the rear frame tubes 35 and lower main frame tubes 17, is connected between the rear frame tubes 35 of the frame 10 and the cross tube 50 connecting the upper main frame tubes 16. It may be observed that each additional tube 30 is connected to an opposed end of cross tube 50. Further, it may be observed that the connection of the additional tubes 30 to cross tube 50 means that, whilst the additional tubes 30 extend a substantial proportion of the distance between the rear frame tubes 35 and steering head mounting tube 15, they do not span the whole distance.

Connection between additional tubes 30 and cross tube 50 may be secured by gusseting of each additional tube 30 to each upper main frame tube by a gusset 32 to impart greater rigidity. The area and thickness of the gussets 32 may be dictated by the desired stiffness of the frame 10. The gussets 32 may be the only gussets used in the frame 10. The stiffness or rigidity of the frame 10 is dictated by the desired handling characteristics of the motorcycle incorporating the frame 10, the motorcycle 70 being shown in Figure 8. A number of parameters will need to be taken into account when judging the handling characteristics of the motorcycle 70. The proposed use for the motorcycle 70 as well as its weight, are two factors to be considered.

The main frame tubes 16, 17 have a downward gradient from the steering head mounting tube 15. The lower ends of lower main frame tubes 17 join the upper main frame tubes 16 and opposed portions swing arm pivot mountings 42 and, beneath these, footpeg/pedal mountings 40 are connected to the upper main frame tubes 16 in this region of the frame 10 which also incorporates additional rear frame members 39. As may be seen conveniently from Figures 3 and 4, a rear wheel swing arm 80 and rear shock absorber 90 are connected to the frame 10 in this region. Both swing arm 80 and shock absorber 90 are important parts of the motorcycle suspension and they are subject to shock forces during operation of a motorcycle 70 incorporating the frame as above described. Swing arm 80 serves a further purpose in that it mounts an axle for the rear wheel of the motorcycle. It may be understood that rear wheel swing arm 80 pivots about pivot mountings 42 during operation of the motorcycle.

In a conventional trellis frame, such shock forces would be translated into the main frame tubes 16, 17 and so on into the engine 72 which is a fully stressed member of the frame 10.

However, the inclusion of the additional tubes 30, as shown in the Figures, results in a distribution of force, translated into the rear frame tubes 35, in the region of the lower shock absorber -swing arm 80, 90 mounting, and upper shock absorber pivot mounting 75, also called the shock pivot, to the additional tubes 30 and on to the cross tube 50 such that the main frame 12 is substantially released or discharged from shock forces during operation of a motorcycle incorporating the frame 10.

To this end, the additional tubes 30 form a direct or a nearly direct joint from the rear frame tubes 35, and upper shock absorber pivot mounting 75, which takes the shock forces from the rear wheel swing arm 80 and shock absorber 90 to the steering head mounting tube 15. This direct or nearly direct joint is illustrated by arrow "A" in Figure 2. That is, shock forces - or a majority of the shock forces translated from the rear wheel swing arm 80 and the rear shock absorber 50 -through swing arm (or swing fork) mountings 42, and upper shock absorber pivot mounting 75, to the frame 10, during operation of a motorcycle 70 incorporating it, as illustrated in Fig. 8, is directed along the additional tubes 30, to the cross tube 50 and the steering head mounting tube 15, and not significantly into the lattice structure of the main frame 12. In this way, the main frame 12 may be released or discharged from shock forces, as may the engine, with benefit in handling terms.

The frame 10 also incorporates forged components to further facilitate time efficient mass production. Forged components may include the upper shock absorber mounting 75 and the steering head mounting tube 15 as well as other joints in the frame 10.For example the swing arm pivot mountings 42,and the footpeg/pedal mountings 40 may be forged components as may the upper shock absorber mounting on the frame 10. Use of forged joints facilitates robotic welding and more precise location of welds during fabrication.

The swing arm pivot and footpeg/pedal mountings 40 and 42 each have respective portions on each side of the frame 10 correspondent with right and left hand sides of a motorcycle. These portions 40a, 40b, 42a, 42b, conveniently shown in Figures 5 and 6 and which are conveniently of sheet metal having little stiffness in a sideways direction though, in order to reduce assembly stresses when the rear wheel swing arm 80 is clamped to the frame 10 and increase sideways stiffness, a stiffening tube 60 is disposed, and joined to the portions, between the swing arm pivot portions 42a and 42b.

The tubes of the frame 10 have a elliptical or oval and circular shape, an elliptical shape being particularly desirable. However, tube cross sections of other shape including polygonal cross section could be employed. Joining of the various tubes within the lattice structure of frame 10 is conveniently performed by welding with robotic welding being particularly preferred due to its precision and ready adaptability to mass production. If necessary, welds may be finished by machining, such as laser trimming, to ensure still further precision. Whilst a range of materials may be used for the frame tubes, steel is an especially suitable material.

The motorcycle frame 10 has a high degree of rigidity in the vertical, frontal and lateral directions while minimising the weight of the frame 10. At the same time, the engine - when mounted to the main frame 10 - is subject to a lower magnitude of shock forces arising during operation than previous frame designs. Further, the frame 10 achieves these benefits whilst maintaining a slender appearance for a motorcycle with desirable handling characteristics and whilst reducing assembly stresses when engine and swing arm 80 are mounted to the frame 10.

Modifications and variations to the motorcycle frame of the present invention may be apparent to the skilled reader of this disclosure. Such modifications and variations are to be deemed within the scope of the present invention.

WE CLAIM:

1. A motorcycle frame (10) comprising a lattice of tubes extending rearward from a steering head mounting tube (15), the lattice including a main frame (12) comprising main frame tubes (16,17) and rear frame tubes (35) with frame struts (18) linking the main frame tubes (16) wherein at least one additional tube (30) is provided to extend in a direction between the rear frame tubes (35) and the steering head mounting tube (15).

2. A frame (10) as claimed in claim 1 wherein said main frame tubes (16,17) form a structure comprising paired upper and lower main frame tubes (16,17) oriented, along at least portion of their lengths, substantially parallel to each other.

3. A frame (10) as claimed in claim 2 wherein said upper main frame tubes (16) have larger cross sectional area than the lower main frame tubes (17).

4. A frame (10) as claimed in claim 2 or 3 wherein said at least one additional tube comprises a pair of additional tubes (30), each additional tube (30) being connected, either directly or indirectly, to at least one of said upper main frame tubes (16).

5. A frame (10) as claimed in claim 4 wherein each additional tube (30) is connected to a cross tube (50) extending between the upper main frame tubes (16).

6. A frame (10) as claimed in claim 5 wherein each additional tube (30) is connected to a corresponding end of the cross tube (50).

7. A frame (10) as claimed in claim 5 or 6 wherein said cross tube (50) is gusseted to at least one of said upper main frame tubes (16).

8. A frame (10) as claimed in any one of claims 2 to 7 wherein forward portions (16a) of the main frame upper tubes (16) converge in the direction of the steering head mounting tube (15).

9. A frame (10) as claimed in claim 8 wherein forward portions (17a) of the lower main frame tubes (17) converge in the direction of the steering head mounting tube (15).

10. A frame (10) as claimed in claim 9 wherein an angle of the aperture (19) between the converging upper and lower main frame tubes (16,17) is a function of the rigidity required of the frame structure and the dimension and shape of engine and other components to be mounted on the frame (10).

11. A frame (10) as claimed in any one of the preceding claims wherein said additional tube(s) (30) form a direct or nearly direct joint from the shock absorber-swing arm mounting (75, 80, 90) to the steering head mounting tube (15).

12. A frame (10) as claimed in claim 11 wherein said additional tube(s) (30) span less than the whole distance between the shock absorber-swing arm mounting (75, 80, 90) and the steering head mounting tube (15).

13. A frame (10) as claimed in any one of the preceding claims wherein, when an engine (72) is mounted to the mainframe (12), the engine (72) forms a stressed member of the frame (10).

14. A frame (10) as claimed in any one of the preceding claims comprising swing arm pivot and footpeg/pedal mountings (40, 42) each having respective portions (40a, 40b, 42a, 42b) on each side of the frame (10) correspondent with right and left hand sides of a motorcycle 70), a stiffening tube (60) being disposed, and joined to the portions (40a, 40b, 42a,42b) between the swing arm pivot portions (42a, 42b).

15. A motorcycle (70) incorporating a frame (10) as claimed in any one of the preceding claims.