WO2020089226A2

WO2020089226A2 - Motorcycle suspension system

Info

Publication number: WO2020089226A2
Application number: PCT/EP2019/079527
Authority: WO
Inventors: Mark Truman
Original assignee: ARC Vehicle Limited
Priority date: 2018-10-29
Filing date: 2019-10-29
Publication date: 2020-05-07
Also published as: GB2578468A; WO2020089226A3; GB201817631D0; GB2578468B

Abstract

The present invention provides a motorcycle (100) having a front wheel suspension system (104) with a swing arm (118) and a hub centre steering system (108).

Description

Motorcycle suspension system

The present invention relates to a motorcycle suspension system. More specifically, the present invention relates to a motorcycle front swing-arm suspension system.

The term "motorcycle" will be used throughout. It will be understood that this term does not limit the invention to any particular motive power source. The invention is suitable for motorcycles powered by internal combustion engines (1C engine motorcycles), those powered by electric motors having onboard batteries (electric motorcycles), combinations of the two (hybrid motorcycles) and motorcycles with other power sources (e.g. fuel cells).

The most common form of front-wheel suspension on motorcycles is a telescopic fork arrangement. This comprises an angled telescopic damper and spring arrangement. Despite being widely adopted by the motorcycle industry, front forks have several inherent drawbacks. Firstly, they are very prone to "brake dive". Under braking, load is passed from the rider and body of the motorcycle, through the front forks to the front wheel (which is in frictional contact with the ground). This tends to compress the forks, which contract, lowering the front of the motorcycle and tipping it forward. Although various solutions have been proposed to this problem, it remains an inherent design feature of telescopic forks. It should be noted that although brake dive can be disconcerting for the rider, and risks bottoming out the forks, there is a benefit in terms of reducing the wheel base (horizontal distance between wheel centres), which in turn improves responsiveness in turning the motorcycle. Another problem with telescopic forks is that they are typically raked, which provides the steering axis of the front wheel away from vertical and produces a rake (angle of the steering axis) and trail (horizontal distance between the wheel-ground contact point and the intersection of the steering axis with the ground). Excessive trail can make steering difficult. A further problem is that due to the rake angle, the forks create a lever-arm about the pivot (headstock) which requires them to be able to withstand a high degree of bending load. This means they must be robust, adding weight to the motorcycle. A further consequence is that fork steering and suspension systems have to run a greater steering (rake) angle than is ideal.

Swing-arm (or "swinging arm") suspension systems are also known in the art of motorcycle design. Many motorcycles utilise swing-arms, and almost all cases these are found on the rear wheel of the motorcycle.

Although uncommon, front swing-arms have been proposed. One advantage of such systems is they permit hub-centre steering to be employed. The bimota (TM) TESI (TM) is one example of a motorcycle with a front swing-arm suspension system and hub-centre steering. IT1171971 and US5133223 (Bimota S.P.A.) describe hub-centre steering systems with a swing arm.

Front swing-arm suspension systems comprise a swing-arm (which may be one or two-sided) attached to the motorcycle body about a transverse, horizontal swing-arm pivot axis. The wheel is mounted (via the hub centre steering system) to the other end of the swing-arm for rotation about a transverse, horizontal front wheel axis. In motor cycles with hub-centre steering, the front wheel axis is rotatable itself about a generally vertical steering axis. Therefore trail can be selected to provide the best performance.

A problem with front swing-arm suspension motorcycles, including that of US5133223, is that the swing arm is mounted at a front-down inclination angle. This means that at rest, or static sag, the front wheel axis is positioned vertically below the swing-arm axis. This is problematic because under braking, the swing arm tends to rotate relative to the motorcycle body. In particular, the wheel axis tends to move upwards relative to the swing-arm axis. This causes an extension in the wheel base. This is problematic for two reasons. Firstly, it decreases the agility of the motorcycle when it is usually needed (for turning), and secondly it is the opposite effect to what most riders are used to (shortened wheel base under braking). This means that the dynamics of the motorcycle will feel unfamiliar to the seasoned rider and that anti dive, which feels unnatural to the rider, is provided.

A further problem with front swing-arm systems, for example in US5133223, is that it is necessary for the swing arm to be part of a quadrilateral, or four-bar, linkage. This ensures that the steering axis remains vertical (or as close to vertical as possible) through travel of the swing arm. This additional componentry adds weight to the suspension system, which is undesirable.

GB559441 discloses a castor-action self-centring spring-framed motorcycle from 1943. A pair of front arms I are provided that support the front wheel, although the operation of the steering system is not disclosed. Further, it will be noted that the two steering arms referred to as "double arm steering Y" are inclined downwardly towards the front of the vehicle, which would produce some very odd steering geometry as the suspension is compressed, and possibly even a negative rake which would make the vehicle highly unstable.

GB2191158 discloses a motorcycle with swing arm front suspension. This motorcycle design uses a steering system in which the steering axis does not pass through the wheel centre. This is undesirable as it creates unexpected handling characteristics when steering. Further, the motorcycle has a complex linkage arrangement to connect the handlebars to the front wheel for steering. Still further, the swing arm is provided proximate the wheel's position of greatest travel meaning that a large clearance has to be provided, making the swing arm project from the vehicle in a lateral sense.

US4741545 discloses a motorcycle with a front swing arm, although the swing arm is not concentric with the wheel hub, nor is the steering axis. Similarly US5782313 and US 4756379 have steering axes offset from the wheel hub.

It is an aim of the present invention to overcome, or at least mitigate the above problems.

According to a first aspect of the invention there is provided a motorcycle comprising: a body; a front wheel mounted on an axle, the axle defining an axle axis; a front wheel suspension system comprising a swing arm, the swing arm attached to the body to pivot relative thereto about a swing arm pivot axis at a first position on the swing arm, and attached to the axle at a second position on the swing arm spaced apart from the first position; wherein the front wheel suspension system is configured such that the axle axis is positioned vertically higher than the swing arm pivot axis when the motorcycle is at a static sag condition with unladen mass.

By "static sag" condition we mean a condition of the motorcycle when it is at rest, and the suspension system is partially compressed under the mass of the motorcycle. In this condition, the mass of the motorcycle is the "unladen mass" as defined in Council Directive 93/93/EEC of 29 October 1993 on the masses and dimensions of two or three-wheel motor vehicles.

Advantageously, this means that the wheel base will become shorter under braking, which overcomes the problems with the prior art. Furthermore, the combination of the inclined swing arm suspension and hub-centre steering provides better handling, particularly under braking and turning compared to the prior art. It also provides for a very compact and lightweight steering and suspension system.

In a preferable embodiment, a hub-centre steering system is provided and configured to steer the front wheel about a steering axis. This provides the combined effect of a shortened wheel base under braking, as well as the geometrical stability of having the steering axis at the centre of the wheel. This enhances rideability and performance e.g. when steering under, or after, braking.

According to a second aspect of the invention there is provided a motorcycle comprising: a body; a front wheel; a suspension system; handlebars; and, a front wheel hub-centre steering system for transferring a steering torque from the handlebars to the front wheel, the hub-centre steering system comprising: a hub subassembly on which the front wheel is mounted for rotation about a front wheel rotation axis; an axle subassembly attached to the suspension system; wherein the hub subassembly is pivotable about a steering axis, relative to the axle subassembly to steer the front wheel; and, an upright in a load path from the handlebars to the hub subassembly, the upright comprising a mudguard covering part of the outer surface of the front wheel.

In other words, the upright (being unitary with the mudguard) forms part of the steering load path. This arrangement permits a close-to-vertical steering axis (reducing rake and trail) and reduces the need for additional components in the form of a mudguard.

An example motorcycle with a suspension system according to the invention will now be described with reference to the Figures in which:

Figure 1 is a right-hand side view of a motorcycle having a suspension system according to the present invention;

Figure 2 is a left-hand side view of the motorcycle of Figure 1;

Figure 3 is a right-hand side view of detail of the front end of the motorcycle of Figure 1;

Figure 4 is a left-hand side view of detail of the front end of the motorcycle of Figure 1;

Figure 5 is a right-hand side view of the steering and suspension systems of the motorcycle of Figure 1;

Figure 6 is a top side perspective view of selected components of the suspension system of motorcycle of Figure 1;

Figure 7 is an underside perspective view of selected components of the suspension system of motorcycle of Figure 1; Figures 8 to 10 are side views of the steering and suspension systems of the motorcycle of Figure 1 in a static sag, full droop and bump condition respectively;

Figures 8a to 10a are side views of the steering and suspension systems of the motorcycle of Figure 1 in a static sag, full droop and bump condition respectively;

Figure 11 is a perspective view of the steering system of the motorcycle of Figure 1;

Figure 12 is a side view of the steering system of the motorcycle of Figure 1;

Figure 13 is a detail view of a part of the steering system of the motorcycle of Figure 1;

Figure 14 is a detail view of a part of the steering system of the motorcycle of Figure 1;

Figure 15 is a detail view of components of the steering system of the motorcycle of Figure 1; and,

Figures 16 and 17 are detail views of subassemblies of the steering system of the motorcycle of Figure 1

General assembly

Referring to the Figures, there is provided a motorcycle 100. The motorcycle 100 has a generally accepted frame of reference, in which "front" and "rear" are defined with respect to the forward direction of travel, "up" and down" are defined as the directions when the bike is upright and stationary, and "left" and "right" from the rider's perspective. These terms will be used in the present application, and it will be understood that such terms refer to the motorcycle in use.

The motorcycle 100 comprises a body 102, a front suspension 104 connecting the body 102 to a front wheel 106, a steering system 108, and a rear suspension 110 connecting the body 102 to a rear wheel 112.

Body 102

The body 102 will not be described in detail here, but briefly comprises a monocoque frame 114 containing a battery and electric motor for providing torque to the rear wheel 112 via a chain 116. In this embodiment, the motorcycle 100 is an electric motorcycle, but it will be noted that the battery and electric motor could be replaced with an 1C engine, fuel cell or similar.

Front suspension 104

The front suspension 104 comprises a front swing arm 118 and a sprung damper 120. These are shown in detail in Figures 5 to 7.

The swing arm 118 comprises a first (right) arm 122, a second (left) arm 124 and a crossbar 126. The first arm 122 comprises a forward section 128, an intermediate section 130 and a rearward section 132. Each of the sections 128, 130, 132 is generally straight, providing the first arm 122 with an inverted U-shaped appearance in profile (Figure 5). At a first end of the forward section 128 there is provided a front axle receiving formation 134 in the form of a bore. A front-most portion 136 of the first arm 122 is detachable, with the first arm 122 and the portion 136 each forming part of the bore 134. At a second end of the forward section 128, the forward section 128 joins a first end of the intermediate section 130. At a second end of the intermediate section 130, it joins a first end of the rearward section 132. A spring damper attachment formation 140 is provided at the intersection of the intermediate section 130 and rearward section 132. A swing arm mounting formation 138 is provided at a second end of the rearward section 132.

The second arm 124 is a mirror image of the first arm, and comprises a forward section 142, an intermediate section 144 and a rearward section 146. Each of the sections 142, 144, 146 is generally straight, providing the second arm 124 with an inverted U-shaped appearance in profile (Figure 7). At a first end of the forward section 142 there is provided a front axle receiving formation 148 in the form of a bore. A front-most portion 150 of the second arm 124 is detachable, with the second arm 124 and the portion 150 each forming part of the bore 148. At a second end of the forward section 142, the forward section 142 joins a first end of the intermediate section 144. At a second end of the intermediate section 144, it joins a first end of the rearward section 146. A swing arm mounting formation 152 is provided at a second end of the rearward section 146. No spring damper attachment formation is provided on the second arm 124.

The crossbar 126 extends between the first and second arms 122, 124, normal thereto, thus forming an "FI" shape in plan. The crossbar 124 is generally flat having a forward-facing concave shape. The crossbar 126 extends between the opposing intermediate sections 130, 144 and rearward sections 132, 146.

The arms 122, 124 are parallel and aligned such that: the front axle receiving formations 134 lie centred on a front wheel axle axis A, and the swing arm mounting formations 138, 152 lie on a swing arm mounting axis B.

The sprung damper 120 is well known in the art and will not be described in detail. It generally comprises an extensible, telescopic damper 154 having a cylinder 156 and a piston 158 moveable therein and relative thereto. The cylinder 156 has a body attachment formation 160 and the piston has a swing arm attachment formation 162. A compression spring 164 urges the piston 158 from the cylinder 156 (i.e. into an extended position). Referring to Figure 3 the front wheel 106 is attached to the front swing arm 118 via the steering system 108 (to be described below). The wheel is centred on the front wheel axle axis A, and rotates about the axis A when the steering condition is "centred". It is important to understand at this stage is that the swing arm 118 and wheel 106 move together in a vertical and horizontal sense (although as will be explained, the wheel 106 does have some rotational degrees of freedom).

The swing arm 118 is mounted to the body 102 to rotate relative thereto about the swing arm mounting axis B. The arms 122, 124 straddle the body 102 and are attached at either side thereof. In the present embodiment, there are two individual, axially-aligned rotational joints- one per arm where the swing arm attaches to the body. In an alternative embodiment, there may be a common joint and / or axle extending between the arms and engaging the body 102. The sprung damper 120 is connected to the body at a body sprung damper mounting point 166, and to the swing arm 118 at the swing arm sprung damper attachment point 140.

Referring to Figure 5, which like Figure 1 to 4 shows the motorcycle 100 in a "static sag" condition, the swing arm 118 is mounted to the body 102 such that the horizontal level FIB of the axis B is vertically below the horizontal level HA of the axis A. In this position the sprung damper 120 is near horizontal. Referring to Figure 1, a swingarm axis SX defined in the XZ (vertical) plane joining the axle axis A and the swing arm axis B will subtend a swing arm angle Y with the horizontal. In this case, Y = 9 degrees. This static sag condition is also shown in Figure 8, where the vertical distance between the level of axis B, FIB and the level of the axis A, FIB is indicated at Dl.

Figure 9 shows the swing arm position in full droop, that is with the motorcycle suspended from the ground. Under these conditions, the swing arm has rotated about the axis B in a clockwise direction (i.e. front end down or wheel down). This has the effect of reducing the vertical distance D2 between the axes A and B, but as can be seen, axis A remains above axis B, such that D2<D1.

Figure 10 shows the motorcycle at bump condition- i.e. with the front wheel at its highest possible position relative to the body, or "fully compressed". Under these conditions, the swing arm has rotated about the axis B in an anticlockwise direction relative to Figures 8 and 9 (i.e. front end up or wheel up). This has the effect of increasing the vertical distance D3 between the axes A and B, such that D3>D1.

Figures 9 and 10 represent the extremes of travel of the assembled suspension system 104, and as can be seen at all such conditions (full droop to bump) the axis A remains vertically above axis B.

Front wheel 106 The front wheel 106 is conventional, aside from the hub-centre steering system which will be discussed below.

Steering system 108

The steering system is a hub-centre system, of a similar type to that disclosed in US5133223.

Referring to Figure 11, the steering system 108 comprises handlebars 168, a headstock 170, a hinge joint 172, a wishbone 174 a front upright 176, left and right caliper mounts 178, 180, an axle subassembly 182 and a hub subassembly 184.

The handlebars 168 are conventional and will not be described in detail. The handlebars are mounted for rotation relative to the headstock 170 about a steering axis S (Figure 5) which intersects the front wheel axle axis A.

The headstock 170 is mounted to the body 102.

Referring to Figure 13, the handlebars 168 comprise a shaft 186 which extends through the headstock 170. Underneath the headstock 170, the shaft 186 is attached to a collar 188. The collar 188 comprises a pair of opposed hinge pivots 190, 192 which extend radially outwardly therefrom.

The hinge joint 172 (also known as a "scissor") comprises a first hinge part 194 and a second hinge part 196. The first part 194 is generally "Y" shaped having a body 198 and two opposed wings 200, 202. The second part 196 is generally "FI" shaped having two parallel, offset arms 204, 206 and a crosspiece 208.

The first hinge part 194 and the second hinge part 196 are attached to rotate relative to each other about a hinge joint axis HJ . The arms 204, 206 of the second part are positioned on either side of the body 198 of the first part 194. The hinge joint axis HJ is horizontal, lateral (i.e. running from left to right) and normal to the steering axis S.

In a further, preferred, embodiment, the single-axis rotational joint shown in Figure 13 (with a single degree of freedom in rotation about HJ) is replaced by a joint having at least one further degrees of rotational freedom (i.e. about the fore-aft horizontal axis). This allows greater articulation of the joint 172 and reduces the likelihood of jamming. The joint may be a universal joint ("UJ").

Each wing 200, 202 of the first hinge part 194 is attached to a respective hinge pivot 190, 192 for rotation relative thereto about an upper hinge axis HU. The upper hinge axis HU is horizontal, lateral (i.e. running from left to right) and normal to the steering axis S. The wishbone 174 is generally "Y" shaped comprising a pivot lug 210, a first arm 212 and a second arm 214. The wishbone 174 is mounted to the body 102 at the arms 212, 214 for rotation about a wishbone pivot axis W (see Figure 3). The wishbone pivot axis W is lateral (i.e. running from left to right) and normal to the steering axis S. The wishbone 174 moves between extremes of travel in which is it horizontal (full droop, Figure 9) and tilted upwardly (full bump, Figure 10). At all positions (including static sag, Figure 8) the front end of the wishbone (pivot axis HL) is in line with, or above, the wishbone pivot axis W. In other words, the inclination of the wishbone 174 is the same as the swing arm 118 (upwards, towards the front of the vehicle). At no point across the normal range of travel are the wishbone or swing arm tilted downwardly.

The front upright 176 comprises a body 216, two lugs 218, 220 and two arms 222, 224. The body 216 is shaped as a mudguard. In particular it is concave facing the wheel such that the wheel can at least partially enter it. In other words, the wheel is received in the body 216. The body 216 has a curved surface region 218 with a first side panel 221 and a second side panel 223. The curved surface region 218 describes a circle segment CS which, in use, is subtended about the wheel rotation axis.

The lugs 218, 220 extend from a convex side of the body 216.

The arms 222, 224 extend from the side panels 220, 221 in a generally radial direction and terminate at respective free ends 226, 228.

Referring to Figure 13, the arms 204, 206 of the second hinge part 196 are positioned either side of the pivot lug 210 of the wishbone 174. This assembly is positioned between the lugs 218, 220 of the upright 176. A shaft (not visible) is provided to permit relative rotation of the second hinge part 196 and the upright 176 about a lower hinge axis HL. The lower hinge axis HL is horizontal, lateral (i.e. running from left to right) and normal to the steering axis S. The pivot lug of the wishbone 174 is attached to the shaft by a universal joint 175 which is able to move in all three degrees of rotational freedom.

It will be seen comparing Figures 8 to 10, that movement of the front wheel 106 relative to the body 102 is permitted by this arrangement. In particular, movement of the upright 176 (which is attached to the wheel as will be described below) relative to the headstock 170 is permitted by articulation of the hinge joint 172 from a fully extended condition in Figure 9 (where the parts 194, 196 are almost aligned, and have an internal angle Z of just under 180 degrees) to the fully compressed condition of Figure 10 (where is parts 194, 196 are folded or hinged against one another and have an internal angle Z near zero degrees). At static sag (Figure 8), Z is about 90 degrees. Referring to Figures 8a to 10a (which mirror Figures 8 to 10), a quadrilateral Q linking the pivoted ends of the wishbone 174 and swing arm 118 is formed. As described above, the wishbone 174 and swing arm 118 maintain the same orientation / inclination and neither tilts downward towards the front of the vehicle across the range of movement of the suspension system. At full droop (Figure 9a), the wishbone 174 is horizontal (whilst the swing arm 118 remains inclined upwardly).

Turning to Figure 14, the left and right caliper mounts 178, 180 are shown assembled with the axle subassembly 182 and the hub subassembly 184. The caliper mounts 178, 180 are mirror images of each other, and visible in isolation in Figure 15. The caliper mount 178 comprises an annular body 230 having an elongate central aperture 232. An upright attachment boss 234 is positioned at a first position of the body 230. A caliper attachment arm 236 is positioned at a second position on the body diametrically opposed to the first position. In use, a brake caliper is attached to the arm 236.

The assembled hub subassembly 180 and axle subassembly 182 are shown in Figure 16. The axle subassembly 182 is shown in isolation in Figure 17.

The axle subassembly 182 comprises an axle 238 defining the front wheel axle axis A. A rotational joint 240 is provided at the midway point of the axle 238 which defines a hub steering axis FIS, which when assembled is coincident with the steering axis S.

The hub subassembly 184 defines a wheel rotation axis WR, which represents the axis of rotation of the front wheel 106 when mounted to the hub subassembly 184. The hub subassembly 184 is mounted to the rotation joint 240 in the axle 238 such that is can rotate relative thereto about the hub steering axis FIS. As a result, the wheel rotation axis is also rotatable about the hub steering axis (they are perpendicular). It will be noted that in the centred condition of the steering system (as shown in Figure 16) the wheel rotation axis WR and wheel axle axis A are coincident.

The left and right caliper mounts 178, 180 are mounted to either side of the hub subassembly for movement therewith. The axle 238 is mounted to the front axle receiving formations 134, 148 of the swing arm 118.

The free ends 226, 228 of the arms 222, 224 are attached to the upright attachment bosses 234 of the caliper mounts 178, 180.

Rear suspension 110

The rear suspension 110 is a swing arm suspension system, and will not be discussed in detail here.

Rear wheel 112

The rear wheel 112 is conventional and will not be discussed further. Performance - suspension

The above-described motorcycle is configured to provide a shortening of the wheel base and trail under braking. Referring to Figure 5, under braking the mass of the body 102 and rider will tend to produce a torque on the body 102 about the swing arm pivot axis B. The body and rider will "dive" towards the front wheel. The swing arm therefore rotates relative to the body in the opposite direction R. The swing arm pivot axis B becomes lower relative to the axle axis A. As the swing arm rotates, the sprung damper is compressed. Aside from the fact that the sprung damper is generally horizontal and only on a single side of the vehicle, the dynamic effects of this system are well understood and will not be described in detail.

Comparing Figures 8 and 10, under brake dive the vertical distance increases from Figure 8 to Figure 10 (D1 to D3). As the swing arm has a rotational degree of freedom only, and because the axle axis A starts (in Figure 8) vertically above the swing arm axis B, the horizontal distance between A and B decreases from H 1 in Figure 8 to FI3 in Figure 10. Referring to Figure 1, this will shorten the horizontal distance between the front and rear wheel axle axes (i.e. the wheel base WB).

The dynamic effect of wheel base shortening is the same as occurs in traditional fork-suspension motorcycles. Therefore the feel of the motorcycle 100 under braking is similar to that of traditional motorcycles.

As discussed, the wishbone 174 never tilts downwards towards the front of the vehicle across the range of motion of the suspension system. Due to the wishbone 174 being horizontal at its lowest position (full droop, Figure 9a), any brake dive will cause upward rotation of the front of the wishbone. This, in turn, ensures that the rake angle R (Figure 1) is maintained and trail is always above zero.

Performance - steering

Use of hub-centre steering allows for rake (R) and trail (T) to be determined according to what is beneficial for vehicle dynamics (per Figure 1).

The hub-centre steering system 108 according to the invention works as follows. When the handlebars are rotated by the rider applying a steering torque ST (Figure 11) about the steering axis S, ST is transferred to the hinge joint 172, which in turn is transferred to the upright 176. Because the free ends of the arms 222, 224 of the upright are attached to the caliper mounts 178, 180, this transfers the torque ST to the hub subassembly 184, rotating it (and the front wheel 106) about the steering axis S). It will be noted that the hinge joint is attached to the upright 176 at the lugs 218, 220. As such, the steering torque is applied to the wheel outside the perimeter of the wheel (when viewed along the wheel axis). This makes for a compact arrangement. The steering system 108 maintains this capability as the suspension system adjusts. Referring to Figures 8 to 10, movement of the front wheel relative to the body (as the suspension moves) tends to extend and contract the hinge joint 172 to vary the internal angle Z. The wishbone 174 also pivots to account for movement of the top of the upright 176 / hinge joint 172 relative to the headstock 170. Although the wishbone 174 cannot pivot about the steering axis S, the provision of the universal joint 175 permits such motion by the hinge joint and upright relative to the wishbone.

It will also be noted that due to the "U" shape of the swing arm 118 it can be positioned closer to the wheel 106. This is because the "U" shape means that the swing arm 118 is not coincident with the region of the wheel 106 which has the highest degree of lateral travel under steering. Referring to Figure 1, the area of the wheel (including the tyre) with the highest degree of lateral travel will be the area of the tyre sidewall furthest from the steering axis S. Because the swingarm 118 is eccentric about its own axis SX (describing a curve, or U-shape away from the swing arm axis SX), then it avoids the area of the wheel with the highest degree of lateral movement. Instead, it passes over a point of the wheel / tyre at a position closer to the steering axis (at approximately 45 degrees to the steering axis S) where lateral movement is less severe. This allows the swing arm 118 to be positioned closer to the wheel 106 than would be possible with e.g. a straight swing arm. This is beneficial for making the motorcycle more compact and aerodynamic.

In use, the hinge joint limits the amount of suspension travel possible. As can be seen comparing the suspension and steering conditions of Figures 9 and 10, at all positions between full droop (Figure 9) and bump (Figure 10) the axis A is vertically above the axis B.

Variations

As discussed above, the wishbone is horizontal in its lowest position (full droop). It is envisaged that it could be upwardly inclined towards the front of the vehicle across the full range of motion (including full droop), like the swing arm.

Claims

1. A motorcycle comprising: a body; a front wheel mounted on an axle, the axle defining an axle axis; a front wheel suspension system comprising a swing arm, the swing arm attached to the body to pivot relative thereto about a swing arm pivot axis at a first position on the swing arm, and attached to the axle at a second position on the swing arm spaced apart from the first position, wherein the front wheel suspension system is configured such that the axle axis is positioned vertically higher than the swing arm pivot axis when the motorcycle is at a static sag condition with unladen mass; and, a hub-centre steering system configured to steer the front wheel about a steering axis.

2. A motorcycle according to claim 1, wherein the swing arm is limited to a predetermined range of travel about the pivot axis, and wherein the axle axis is positioned vertically higher than the swing arm pivot axis over the entire predetermined range of travel.

3. A motorcycle according to claim 1 or 2, wherein a line drawn between the axle pivot and swing arm pivot axis is at a swing arm angle of at least 5 degrees to the horizontal at a loaded static sag condition.

4. A motorcycle according to any of claims 1 to 3, wherein a resilient damper is mounted between the swing arm and the body.

5. A motorcycle according to claim 4, wherein the resilient damper is mounted to the swing arm at a position vertically above the pivot.

6. A motorcycle according to claim 5, wherein an angle of a line drawn between the pivot and the point at which the resilient damper is mounted to the swing arm is within 45 degrees of vertical.

7. A motorcycle according to claim 5 or 6, wherein the resilient damper is mounted to be within 45 degrees of the horizontal in use.

8. A motorcycle according to claim 7, wherein the resilient damper is mounted to the swing arm such that upward movement of the front wheel relative to the body reduces the angle between the resilient damper and the horizontal.

9. A motorcycle according to any preceding claim, in which the swing arm is H-shaped in plan, having a first arm attached to a first side of the front wheel axle, a second arm attached to a second side of the front wheel axle, and a crossbar connecting the first and second arms.

10. A motorcycle according to any preceding claim, in which the swing arm defines a swing arm axis drawn between the axle pivot and swing arm pivot axis, in which the swing arm is eccentric about the swing arm axis in profile.

11. A motorcycle according to claim 10, in which the swing arm is U-shaped in profile.

12. A motorcycle according to claim 10 or 11, in which the swing arm extends above the swing arm axis in use.

13. A motorcycle according to any of claims 10 to 12, in which the wheel defines a region of greatest travel under steering, and in which the swing arm passes over the wheel at a position spaced apart from the region of greatest travel.

14. A motorcycle according to any preceding claim, wherein the hub centre steering system comprises an axle subassembly connected to the swing arm, and a hub subassembly mounted to the axle subassembly such that it is pivotable about the steering axis.

15. A motorcycle according to claim 14, wherein the hub centre steering system comprises an upright connected to the hub subassembly for transferring a steering torque thereto.

16. A motorcycle according to claim 15, wherein the upright comprises an integrated mudguard.

17. A motorcycle according to claim 15 or 16, wherein the swing arm forms part of a four bar linkage, the linkage comprising: the upright; and, a pivotable member extending from the body to the upright; in which an axis of rotation the pivotable member relative to the body is configured to remain parallel with, or horizontally below an axis of rotation of the pivotable member relative to the upright such that the pivotable member has a non-negative upward inclination towards the front of the motorcycle over the entire predetermined range of travel.

18. A motorcycle according to any preceding claim, wherein the hub centre steering system comprising an extensible arrangement in a steering load path, the extensible arrangement being configured to transfer a steering torque between a set of handlebars and the front wheel and being configured to permit a variable distance between the front wheel and the handlebars in use.

19. A motorcycle according to claim 18, in which the extensible arrangement determines the limit of travel of the swing arm.

20. A motorcycle according to claim 18 or 19, in which the extensible arrangement is a hinge joint comprising two hinge members connected by a rotational joint.

21. A motorcycle according to claim 20, in which the extensible arrangement lies on the steering axis.

22. A motorcycle comprising: a body; a front wheel; a suspension system; handlebars; and, a front wheel hub-centre steering system for transferring a steering torque from the handlebars to the front wheel, the hub-centre steering system comprising: a hub subassembly on which the front wheel is mounted for rotation about a front wheel rotation axis; an axle subassembly attached to the suspension system; wherein the hub subassembly is pivotable about a steering axis, relative to the axle subassembly to steer the front wheel; and, an upright in a load path from the handlebars to the hub subassembly, the upright comprising a mudguard covering part of the outer surface of the front wheel.

23. A motorcycle according to claim 22, in which the mudguard is integrated with the upright.

24. A motorcycle according to claim 22 or 23, wherein the mudguard extends forward and rearward of the steering axis.

25. A motorcycle according to any of claims 22 to 24, wherein the steering system comprises an extensible arrangement in the load path, the extensible arrangement being configured to transfer a steering torque between the handlebars and the upright and being configured to permit a variable distance between the front wheel and the handlebars in use.

26. A motorcycle according to claim 25, in which the extensible arrangement is a hinge joint comprising two hinge members connected by a joint rotational about at least one horizontal axis in use.

27. A motorcycle according to any of claims 22 to 26, comprising a pivoting arm connected to the body at a first end, and to the upright at a second end, in which the pivoting arm is connected to the upright via a joint permitting rotation of the upright about the steering axis.