GB2448926A

GB2448926A - Motorcycle with variable front wheel steering rake angle

Info

Publication number: GB2448926A
Application number: GB0708629A
Authority: GB
Inventors: Alan Sleith
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-05-04
Filing date: 2007-05-04
Publication date: 2008-11-05
Anticipated expiration: 2027-05-04
Also published as: GB0708629D0; GB2448926B; WO2008135752A1

Abstract

The motorcycle comprises a frame 4; a steering assembly connected to the frame and having an adjustable rake angle and means for adjusting the angle operable in response to the angle of lean of the motorcycle and optionally also in response to motorcycle speed. The steering assembly is connected to a headstock 14; wherein the headstock is pivotally mounted to the frame 4 below the centre, or more especially at the lower end region, of the headstock 14. An actuator 100 is coupled to the frame 4 and the headstock 14 and can be hydraulic, operated by a servomotor 102 with fluid supplied by two accumulators 104b. The servomotor 102 is controlled by a processor monitoring the lean angle of the motorcycle and optionally the motorcycle speed.

Description

MOTORCYCLE ASSEMBLY AND METHOD OF OPERATING THE SAME

The present invention concerns a motorcycle assembly, in particular an assembly for connecting the front wheel and forks of the motorcycle to the frame of the motorcycle, and a method of operating the same.

Development and improvements in the design of motorcycles is a continuous process, one objective of which is to improve the overall handling and stability of the motorcycle. The need for improved handling and stability of the motorcycle is particularly acute as the speed of the motorcycle increases. One area of particular concern with respect to the high speed stability of a motorcycle is during cornering.

Generally, the front wheel of a motorcycle is supported between a pair of forks extending from the headstock at the front of the frame of the motorcycle. The forks are mounted to a steering column so as to be pivotable about the headstock, in order to allow the motorcycle to be steered by rotation of the handlebars. In the majority of designs, the steering assembly and front forks of a motorcycle extend forwards from the motorcycle at an angle to the perpendicular. A number of aspects of the geometry arising from this forward angle of the front forks and wheel assembly arise, First, the angle of inclination of the steering axis to the vertical, termed the castor angle' or the rake angle' is a determining factor in the ability of the motorcycle to negotiate a curve or bend. ln particular, the turning radius the motorcycle for a given rotation of the handlebars increases as the castor angle increases. Thus, a motorcycle with a large castor angle is more difficult to turn than one with a lower castor angle, that is one with the steering axis closer to vertical.

Second, for a given steering arrangement of a motorcycle, the castor angle will determine the horizontal distance from the contact point of the front tyre on the ground to the point of contact of an extrapolation of the line through the steering axis to the ground. This horizontal distance is termed the trail' of the motorcycle. The trail of the motorcycle is the most influential aspect of the steering geometry and its affect on the overall handling of the machine. The presence of trail in the steering geometry provides the motorcycle with stability in a straight line. For straight line stability, the steering geometry must provide the motorcycle with positive trail, that is the contact point of the tyre on the ground is behind the contact point of the line extrapolated through the steering axis and the ground. This is particularly important as riding speeds increase. In general, larger values of trail provide increased straight line stability. However, increasing the trail will also reduce the ability or ease with* which the motorcycle wifi turn.

Finally, a third factor influencing the handling of the motorcycle is the wheelbase, that is the distance between the contact points of the front and rear tyres and the ground. In general, a longer wheelbase provides the motorcycle with an improved stability when traveling in a straight line, especially at high speeds. In contrast, a shorter wheelbase, while less stable in a straight line, will allow the motorcycle to be turned through curves more easily.

It will be appreciated from the foregoing summary that there can arise a conflict between the preferred steering geometry to provide the motorcycle with stability when traveling in a straight line and the geometry best suited to allow the motorcycle to turn. One solution that has been proposed to overcome this inherent conflict is provide a motorcycle with means for adjusting the angle of inclination of the steering axis.

An early attempt to provide an adjustable steering geometry for a motorcycle is disclosed in GB 570,439. There is disclosed an adjustable steering mechanism for a motorcycle, in which the fork structure is pivoted to the lower end of the steering stem about a transverse axis. A slotted clamp secures the upper end of the fork structure, the arrangement being adjustable by a threaded connection, so as to allow the trail of the motorcycle to be adjusted. Variations in the trail must be made manually using a spanner or the like, while the motorcycle is stationary.

US 4,600,207 discloses a connection of the steering column of a motorcycle to the frame, in which the steering column is pivotally mounted to one end of the steering stem. Us 4,600,207 teaches that the mechanism may incorporate an electric motor and linkage to allow adjustment of the steering angle while the motorcycle is in motion. This adjustment may be made manually by the rider using one or more switches Alternatively, it is suggested that the adjustment of the steering angle may be automatic in response to the speed of the motorcycle. No further details regarding automatic adjustment of the steering angle are given in US 4,600207.

In recognition of the importance of trail to the handling of a motorcycle, US 4,629,205 discloses a motorcycle front fork assembly comprising an articulated linkage arranged to keep variations in the trail to a minimum. No manual or automatic adjustment of the trail using this mechanism is disclosed or suggested.

A variable angle steering system for a motorcycle is disclosed in US 4,700,963. The system comprises a shaft coupled to the front forks. An actuator assembly is connected to the handlebars of the motorcycle and causes the pitch angle of the shaft to change about a fixed pivot assembly in response to changes in the position of the handlebars, thus changing the angle of the front forks.

An adjustable triple tree assembly for a motorcycle is disclosed in US 5,967,538. The assembly comprises an upper tree subassembly with a pivot ball providing two major settings of the rake angle of the front forks. There is no suggestion that this adjustment system could be operated while the motorcycle is moving.

An automatic system for the adjustment of the steering geometry of a motorcycle is disclosed in ES 2030318. The system comprises a shaft in the frame of the motorcycle at the height of the steering arm and transverse to the direction of advance. The arm is actuated by a servo mechanism under the control of a processor The system adjusts the rake angle of the motorcycle in response to measurements of the speed of the motorcycle and the position of the handlebars. To render it adjustable, the steering assembly is connected to the frame by a pivotable headstock. ES 2030318 shows the headstock being pivoted either at its upper end (as shown in Figure 2) or at its central portion (as shown in Figure 2).

It will be seen that various attempts have been made to provide a system for the automatic adjustment of the geometry of the front forks and steering assembly of a motorcycle, while the vehicle is in motion. However, there remains a need for an improved system that provides for an improved handling of the motorcycle both when traveling in a straight line and when cornering.

It has been found that the previous attempts to adjust the angle of the steering assembly of a motorcycle while the vehicle is in motion do not provide a stable or improved handling of the vehicle. As discussed above, the proposed systems for automatic adjustment of the steering angle rely upon, at least in part, the position of the handlebars of the motorcycle. In contrast to the teaching of the prior art documents, it has been found that the position of the handlebars is not an appropriate factor on which to base an adjustment of the steering angle of the motorcycle, while the vehicle is in motion. Rather, it has been found that an improved handling of the motorcycle can be achieved when the angle of the steering assembly is adjusted in relation to the lean angle of the motorcycle.

According to the present invention, there is provided a motorcycle comprising: a frame; a steering assembly connected to the frame and having an adjustable angle; means for adjusting the angle of the steering assembly; wherein the means for adjusting the angle of the steering assembly is operable in response to the angle of lean of the motorcycle.

As noted, the angle of lean is employed in the present invention as the factor for adjusting the angle of the steering assembly. In this respect, the term angle of lean' as used herein is a reference to the angle through which the motorcycle moves through from the vertical position in a direction perpendicular to the longitudinal axis of the vehicle. In addition, references herein to the angle of the steering assembly' and its adjustment are references to the castor angle of the steering assembly and adjustment of the castor angle.

The steering assembly of the motorcycle comprises the front wheel of the vehicle and at least one fork extending downwards and forwards of the frame, with the front wheel being supported on an axle or shaft supported by the lower free end of the fork. Most commonly, the steering assembly comprises a pair of parallel forks, with the axle supporting the front wheel extending between the free ends of the two forks. The upper ends of the fork or forks are typically connected to the headstock portion of the frame. The headstock is a tubular assembly extending in a vertical plane at the front portion of the frame, through which a steering shaft extends. The fork or forks are typically connected to the steering shaft at its upper and lower ends by means of support members, often referred to in the art as trees' or triple trees'.

The steering assembly is pivotable about the frame along a line extending through the longitudinal axis of the steering shaft, allowing the front wheel to be turned to the left or the right when the vehicle is in use. Handlebars for gripping by the rider are typically connected to the upper support member or tree, or in some cases directly to the upper ends of the forks.

In particular, as described above, it is advantageous when turning a corner on a motorcycle to have the castor angle, wheelbase and trail of the vehicle shortened.

Accordingly the motorcycle of the present invention is adapted to reduce the castor angle of the steering assembly, thus reducing the trail and the wheelbase, as the vehicle is inclined from the vertical. In order to provide the improvement in handling when cornering in either direction, the means for adjusting the angle of the steering assembly responds to a change in the lean angle to either side of the vertical.

As noted, the motorcycle comprises a steering assembly having an adjustable angle, that is the steering assembly is adjustable through a range of angles. The angle of the steering assembly may be adjustable in discrete steps, such as a given fraction or whole number of degrees in each step. Alternatively, and most preferably, the angle of the steering assembly may be varied to any angle within the range of adjustment. The adjustment in the angle of the steering assembly must be such as to retain a positive trail and, and as a result will generally be low. Accordingly, the steering assembly is preferably arranged to be adjustable by an angle of from 0 up to 20 , more preferably up to 15 . A lower range of adjustment, for example up to 100, or from 0 to 50, may be applied, if found suitable.

The steering assembly may be of any suitable configuration that allows the angle of the steering assembly to be adjusted by the adjustment means. One preferred arrangement is to provide the steering assembly with a connection to the frame of the motorcycle that is adjustable in terms of the angle that the steering assembly extends from the frame. In a particularly preferred arrangement, this adjustable connection is provided by having the headstock, through which the steering shaft extends, mounted so as to be pivotable about a horizontal, transverse pivot extending across the frame. The headstock may be pivoted at any position along its length. However, as will be described hereinafter, a preferred embodiment of the present invention is one in which the headstock is pivoted at its lower end portion.

The motorcycle of the present invention further comprises means for adjusting the angle of the steering assembly in response to a change in the lean angle of the vehicle. This means may be any suitable arrangement that acts upon the steering assembly to change its angle. In a preferred embodiment, the means for adjusting the angle of the steering assembly comprises an actuator mounted to the frame of the motorcycle and operating to move the steering assembly to the requisite angle in response to a change in the lean angle of the vehicle. Any suitable actuator may be employed, for example an electrical, electro-mechanical or mechanical actuator and are known in the art. A particularly preferred actuator mechanism is a hydraulic actuator system. The hydraulic actuator system may operate using oil from the lubrication system of the motorcycle. Alternatively, the hydraulic actuator system is provided with its own hydraulic fluid system having its own reservoir. In a preferred arrangement, the actuator is powered by a servo, fed with hydraulic fluid from an accumulator. Hydraulic fluid under pressure is provided to the accumulator from a hydraulic pump drawing fluid from the reservoir. Low pressure hydraulic fluid from the servo is returned to the reservoir. The hydraulic fluid pump is preferably powered by a power take-off means from the engine of the motorcycle, for example a shaft, sprocket or belt drive from an appropriate part of the engine, for example the crankshaft.

A particularly preferred actuator system comprises an actuator activated by a servo fed from a pair of accumulators.

The actuator assembly for adjusting the angle of the steering assembly may be mounted in any suitable position and orientation to the frame, so as to move the steering assembly as required. In a preferred arrangement, the actuator assembly is mounted substantially horizontally, such that the actuator provides a substantially horizontal force acting upon the steering assembly. A preferred location for the actuator assembly is the upper region of the frame.

As noted above, a particularly preferred arrangement for the adjustable steering assembly is one in which the steering assembly is mounted to a pivotably mounted headstock In this arrangement, the actuator assembiy is preferably connected to the headstock, at a suitable position distanced from the pivot. The actuator mechanism may be connected to any suitable part of the headstock.

However, with the preferred arrangement of having the headstock pivotable about a pivot at its lower end portion, the actuator mechanism is preferably connected to the upper end portion of the headstock. In this way, the greatest mechanical advantage for moving the steering assembly is obtained, in turn allowing a less powerful actuator assembly to be employed.

As noted, the actuator assembly is mounted to the frame. This mounting may be a rigid mounting. However, given that the actuator is operating to move the steering assembly through an arc, the mounting of the actuator assembly to the frame is preferably flexible, in particular one in which the actuator assembly is pivotable about its mount to the frame.

The description hereinbefore has referred to a single actuator and actuator assembly for moving the steering assembly. It will be appreciated that the motorcycle may comprise a plurality of actuator assemblies, for example a pair of actuator assemblies with one assembly attached to the steering assembly or the headstock on each opposing side of the pivot, such that the actuators apply an equal but opposing action to the steering assembly when being moved.

The means for adjusting the angle of the steering assembly is operable in response to a change in the angle of lean of the vehicle. In a preferred arrangement, the motorcycle comprises a sensor for detecting the lean angle of the motorcycle, the sensor generating a signal to control the means for adjusting the angle of the steering assembly. A single sensor for detecting the angle of lean of the motorcycle may be employed. Alternatively, the motorcycle may comprise a plurality of such sensors. Suitable sensors for detecting the angle of lean of the motorcycle are known in the art and include inclinometers, gyroscopic sensors and accelerometers.

The change in the angle of the steering assembly is only required when the motorcycle is moving. Accordingly, the means for adjusting the angle of the steering assembly may be adapted to operate only when the motorcycle is moving. This may be achieved by any suitable means for determining whether the vehicle is moving, for example, by having the means receive information regarding the speed of the motorcycle, in particular from the speedometer system of the vehicle.

In one embodiment, the means for adjusting the angle of the steering assembly is only activated once a predetermined minimum or threshold speed has been reached. In this way, changes in the steering geometry while traveling at low speeds, which could adversely affect the low speed handling or stability of the motorcycle, can be avoided or prevented.

in a particularly preferred embodiment, the angle of the steering assembly is adjusted according to both the angle of lean of the motorcycle and the speed of travel of the motorcycle. Accordingly, in a preferred arrangement, the motorcycle comprises means for adjusting the angle of the steering assembly in response to the angle of lean of the motorcycle and the speed of the motorcycle. In such a case, the motorcycle will comprise one or more means for sensing the angle of lean of the motorcycle and one or more sensors for determining the speed of travel of the motorcycle.

In one embodiment, the motorcycle comprises a processor, the processor arranged to receive signals from sensors measuring both the angle of lean of the motorcycle and its speed. In operation, the processor will generate a signal to activate the actuator on the basis of the angle of lean and the speed of the vehicle.

The use of a processor is particularly preferred when two or more sensors for determining the angle of lean of the motorcycle are being employed.

The motorcycle may be provided with an override facility, whereby the rider may elect to disable the adjustment of the steering assembly angle. The disabling of the adjustment by the rider may operate such that the steering assembly remains fixed at the angle of inclination immediately before being disabled. Preferably, the disabling of the adjustment system will move the steering assembly to a predetermined angle, in particular an angle giving a neutral handling of the vehicle in both a straight line and during cornering. In such a case, with the adjustment system disabled the motorcycle will perform as a conventional motorcycle with a fixed steering assembly. The means for disabling the adjustment may conveniently be routed through the processor, if present.

In addition, the motorcycle may be provided with a means for allowing the user of the vehicle to bypass the automatic control system and/or processor and adjust the angle of the steering assembly manually. This feature will allow a vehicle to be set up more easily, prior to the automatic system becoming active. In addition, during use, the rider may wish to override the automatic adjustment of the angle of the steering assembly and manually adjust the angle, for example in response to a particular maneuver to be made As noted above, a preferred arrangement for having the angle of the steering assembly adjustable is to provide the frame of the motorcycle with a headstock pivotably mounted to the frame, in particular a headstock that is pivotably connected to the frame at its lower end portion. This arrangement has a particular advantage in the operation of the motorcycle. As will be appreciated, by having the headstock pivoted at its lowest end portion, rotation of the headstock about the pivot results in the maximum movement of the upper end of the headstock, compared with locating the pivot at the upper end or centre of the headstock, as shown in ES 2030318. As described above, to improve the handling of the motorcycle, the castor angle is reduced and the wheelbase shortened during cornering. This is achieved by having the headstock rotate to a more vertical position about the pivot. The effect of this is to move the top portion of the steering assembly, in particular the handlebars forwards. This in turn causes the weight of the rider holding the handlebars to move forwards as the turn is initiated. This forwards movement in weight increases the downwards force acting through the front wheel and tyre, resulting in an increase in the grip of the front tyre. An increased grip such as this is of advantage in assisting the motorcycle to turn and can allow corners to be negotiated at higher speeds.

Accordingly, in a further aspect, the present invention provides a motorcycle comprising.

a frame; a headstock pivotably mounted to the frame so as to be rotatable about the mount in a vertical plane; a steering assembly connected to the headstock; wherein the headstock is mounted to the frame at a position below the centre point of the headstock; and means for pivoting the headstock about its mount in response to one or more of the speed of the motorcycle and the lean angle of the motorcycle.

The steering assembly may have its angle adjusted by rotation of the headstock in response to any suitable factor, such as the speed of the motorcycle, the position of the handlebars and/or steering assembly. A particularly preferred arrangement is one where means are provided to rotate the headstock about the pivot in response to the lean angle of the motorcycle, most preferably while the vehicle is in motion, optionally in combination with the speed of the motOrcycle, as hereinbefore described.

As noted, the headstock is pivoted about a position below its centre point. In this respect, the centre point of the headstock is a reference to the position at the centre of the longitudinal axis of the headstock. The headstock is most preferably pivoted at a point in its lowest end portion. As noted, this provides a significant movement of the upper end of the headstock and the handlebars of the motorcycle.

Motorcycles are assembled and sold as complete vehicles. However, in addition to complete vehicles, there is a significant market in parts and components for motorcycles, including motorcycle frames. Accordingly, in a further aspect, the present invention provides a frame for a motorcycle, the frame comprising a headstock and a pivoted mounting for the headstock, wherein the headstock is mounted at a position below the centre point of the headstock.

In addition, it may be decided to modify an existing motorcycle and/or frame to include a pivotable headstock assembly as hereinbefore described. In this respect, the present invention also provides a headstock assembly for a motorcycle, the headstock assembly comprising a headstock mount adapted to be incorporated into the front portion of a motorcycle frame; and a headstock, the headstock being connected to the headstock mount so as to be pivotable about a point in the headstock below its centre point.

References in this respect to the pivot point of the headstock being below' its centre point are to the orientation of the headstock when the headstock assembly is mounted in a frame of a motorcycle. References to the upper' and lower' portions of the headstock are also to be construed accordingly.

As noted above, the presence of an adjustable steering assembly in a motorcycle such that the angle of the steering assembly can be altered, in particular while the vehicle is in motion, in response to a change in the lean angle of the motorcycle allows the vehicle to be operated in a new manner. Accordingly, the present invention provides in a further aspect a method of operating a motorcycle, the motorcycle comprising a steering assembly and means for adjusting the angle of the steering assembly, the method comprising: monitoring the lean angle of the motorcycle; adjusting the angle of the steering assembly in response to changes in the lean angle of the motorcycle.

As previously described, the method preferably operates while the motorcycle is in motion. In one embodiment, the method further comprises monitoring the speed of the motorcycle and adjusting the angle of the steering assembly only once a predetermined minimum speed has been achieved. In this way, changes in the steering geometry that may adversely affect the slow speed handling of the machine are avoided.

In a preferred embodiment, the method further comprises monitoring the speed of the motorcycle and adjusting the angle of the steering assembly according to both the speed and the angle of lean of the vehicle.

As previously described, the method operates to reduce the angle of the steering assembly as the motorcycle negotiates a turn, that is leans at an angle to the vertical to one side or the other. The reduction in the angle of the steering assembly causes the steering assembly to move to a more vertical orientation, reducing the castor angle and the wheelbase of the motorcycle. The reduction in the angle of the steering assembly is preferably greater with higher lean angles.

The method may be applied to reduce the angle of the steering assembly as the lean angle of the motorcycle increases. In this mode of operation, the steering assembly can be considered to have a starting position and angle that is the position of the steering assembly when at rest and the motorcycle is upright in a vertical plane. As the speed of motion of the vehicle increases and the motorcycle begins to lean, the angle of the steering assembly is reduced, as discussed hereiribefore. The steering assembly is returned to this starting position when the motorcycle is returned to the upright position, having completed the turn maneuver.

In an alternative embodiment, the method may employ a starting position, as hereinbefore described, with the angle of the steering assembly being reduced during a turn, as described. In addition, as the speed of the motorcycle increases in a straight line, with the vehicle upright, the angle of the steering assembly may be increased, to increase the wheelbase and castor angle, thus aiding stability and straight-line handling.

As noted above, the ability to adjust the angle of the steering assembly in response to the lean angle of the motorcycle improves the ability of the vehicle to negotiate bends and corners. In addition, the cornering ability of the vehicle is further improved if the ground clearance of the machine is increased when negotiating a bend. Accordingly, it is preferred that the method of reducing the angle of the steering assembly also increases the ground clearance of the vehicle. The system provided by the present Invention in many embodiments, as described hereinbefore, can be arranged to increase the ground clearance of the vehicle, as the angle of the steering assembly is decreased: In addition to assisting the motorcycle to negotiate bends and to corner faster and more efficiently, it has been found that the system of the present invention also has significant applications in the straight line handling of the vehicle, in particular from a standing start, when the system is provided with a means for sensing the speed of travel of the motorcycle and for adjusting the angle of the steering assembly in response thereto.

First, it has been found that the system may be used to adjust the angle of the steering assembly, that is the castor angle, as the motorcycle accelerates from a low speed or moves off from rest. In particular, it has been found that the handling of the motorcycle is significantly improved if the angle of the steering assembly is set to its lowest value in the range, that is the lowest castor angle, when the vehicle is at rest or traveling at a low speed and is increased as the vehicle is accelerated. Similarly, as the vehicle is decelerated from a higher speed to a low speed or brought to rest, the angle of the steering assembly is decreased. Accordingly, in a further aspect, the present invention provides a

method of operating a motorcycle, the method comprising: with the motorcycle moving at a first speed, providing the vehicle with a first steering angle; with the the motorcycle moving at a second speed, greater than the first speed, providing the vehicle with a second steering angle, greater than the first steering angle; as the motorcycle is accelerated between the first and second speeds, adjusting the steering angle between the first angle and the second angle.

With the castor angle of the steering assembly set at its lowest value, the trail of the motorcycle is at its lowest. This improves the maneuverability of the vehicle at low speeds. As the speed of the vehicle increases, the steering angle is increased, in turn increasing the castor angle and the trail, to provide greater straight line stability, as discussed hereinbefore.

In one embodiment, the aforementioned method is used to move the vehicle from a stationary or rest position, in which case the first speed is zero.

The adjustment in the steering angle may be made throughout the entire speed range of the motorcycle. However, in most cases this will be impractical.

Rather, in most cases it is sufficient to have the second speed set as a threshold speed. The threshold speed will thus mark the highest speed at which adjustment of the steering angle will take place. Thereafter, as the speed of the machine increases further, the angle of the steering assembly will remain fixed. Should the vehicle be arranged to have the angle of the steering assembly changed in response to the lean angle of the machine, as described above, such adjustment will occur as the vehicle is turned or corners and moves from the upright position. The effect of this lean will be to reduce the angle of the steering assembly, as described above, in order to improve the cornering performance of the vehicle. Such adjustment will work in conjunction with the change in the steering angle as a result of acceleration between the first and second speeds.

The steering assembly may be moved through any suitable range of angles.

In particular, the steering assembly may be adjustable through an angle of from 0 up to 200, more preferably up to 15 . A lower range of adjustment, for example up to 100, or from 0 to 50, may be applied, if found suitable. The lowest or first angle for the steering assembly will be determined by the geometry of the motorcycle and its intended use A typical first angle is from about 15 to 25 , more preferably about 20 , with the second or higher angle being from about 30 to 40 , more preferably about 35 .

A particularly suitable arrangement for the steering assembly and the motorcycle is as hereinbefore described.

Further, it has been found that adjusting the angle of the steering assembly of a motorcycle from a rest position can improve the performance of the vehicle, in particular when moving from the startline in a race. In general, the practice of making a fast start from a rest position on a motorcycle results in a high acceleration. The arrangement of a motorcycle, in particular position of the engine and the drive being supplied to the rear wheel, causes the front of the vehicle to be raised during acceleration. This results in a reduction in the friction between the front tyre and the road surface. The steering efficiency of the vehicle is also affected. Under high acceleration, such as the start of a race, this can cause the front wheel to lift from the ground (known as a wheelie'). With the front wheel clear of the ground, it becomes impossible to steer the vehicle, It has been found that a motorcycle with an adjustable steering assembly, such as described above, can be operated to reduce this tendency, if the steering assembly is adjusted to its maximum angle when the vehicle is at rest and is thereafter reduced as the vehicle gains speed.

Accordingly, there is provided a method of operating a motorcycle from a rest position, the method comprising: providing the motorcycle with a first angle for the steering assembly with the motorcycle at rest; accelerating the motorcycle; and reducing the angle of the steering assembly from the first angle as the motorcycle accelerates away from the rest position.

By starting the motorcycle from rest with a high steering angle, that is a high castor angle and a long wheelbase, the tendency for the front wheel to rise under high acceleration is reduced. Once the motorcycle is moving, for example above a threshold speed, the angle of the steering assembly is set to a normal running position. In this way, the rider may accelerate at a higher rate than would be possible without the steering angle being increased. Once moving, the motorcycle may operate with a fixed angle for the steering assembly, such as a conventional motorcycle. Alternatively, the vehicle may be provided with a fully adjustable steering assembly, such as hereinbefore described, and operated as described above.

The first angle for the steering assembly may be any suitable angle that reduces the tendency of the front wheel of the motorcycle to rise under high acceleration. A typical angle is from about 300 to 40 , more preferably about 350W The adjustment of the angle of the steering assembly may be carried out automatically and the motorcycle provided with suitable means, including speed sensors and a processor, such as hereinbefore described. Alternatively, the motorcycle may be arranged such that the first angle for the steering assembly is fixed until the rider elects to return the steering geometry to its normal seftings.

A further advantage of operating the motorcycle according to this aspect of the present invention is that, with the angle of the steering assembly set at a high value, the frontal area of the vehicle is reduced, in turn reducing the air resistance and drag. This factor wiH also help the motorcycle accelerate faster from a standing start Embodiments of the present invention will now be described, by way of example only, having reference to the accompanying drawings, in which: Figure 1 is a side view of a representation of a motorcycle according to an embodiment of the present invention; Figure 2 is a perspective view of a representation of a frame for the motorcycle of Figure 1; Figure 3 is a perspective view of a headstock mount incorporated in the frame of Figure 2; Figure 4 is a perspective view of a headstock incorporated in the frame of Figure 2 and mounted to the headstock mount of Figure 3; Figure 5 is a plan view of a portion of the frame of Figure 2 showing details of the actuator assembly; Referring to Figure 1, there is shown in side view a representation of a motorcycle according to the present invention, generally indicated as 2. The motorcycle 2 comprises a frame 4 of known tubular construction, in which is mounted an engine 6. The frame 4 comprises upper frame tubes 8 extending substantially horizontally parallel to the longitudinal axis of the motorcycle. While a frame of known tubular construction is shown in the figures, it is to be understood that the motorcycle and other aspects of the present invention are not limited to such a frame and that the known alternative designs of frame may also be employed without deviating from the principles of the present invention.

A headstock mount assembly 10 is incorporated in the front portion of the frame 4. The headstock mount assembly 10 comprises a headstock mount 12 attached to the front portion of the upper tube frames 8 by conventional means, for example by welding, bolts or a combination thereof. The headstock mount assembly 10 further includes a generally tubular headstock 14 having a central longitudinal bore therethrough, to which is attached a steering assembly, generally indicated as 20, of conventional arrangement. In particular, the steering assembly 20 comprises upper and lower fork mounts 22,24 (trees), mounted to the upper and lower ends respectively of a steering shaft extending through the bore in the headstock 14 (not shown in figures for clarity). A pair of forks 26, again of conventional design, are supported by the upper and lower fork mounts 22, 24 and extend forwards and downwards from the front portion of the frame 4. A front wheel 28 is mounted to the lower, free ends of the forks 26. A conventional handlebar assembly 30 is mounted to the upper end of the steering assembly 20. An actuator assembly 32 is mounted between the upper frame tubes 6 and is connected to the headstock 14, as described below.

The frame 4 is shown in more detail in Figure 2, which is a perspective representation of the frame 4, headstock mount assembly 10 and actuator assembly 32 of the motorcycle of Figure 1. As shown in Figure 2, the frame 4 comprises front and rear cross tubes 34 and 36, extending transversely between the upper frame tubes 6. The headstock mount 12 extends between the front end portions of the upper frame tubes and abuts the front cross tube 34. As shown in Figure 2, the headstock mount 12 comprises a headstock pivot shaft 40 extending transversely across the headstock mount 12 at its lower front portion. The lower portion of the headstock 14 comprises a mount 42 through which the headstock pivot shaft 40 extends, such that the headstock pivots about its lower end portion in a vertical plane. The upper end portion of the headstock 14 comprises a mount 44 for connection to the actuator assembly 32, as described below.

The position of the actuator assembly 32 is clearly shown in Figure 2. The actuator assembly 32 is connected to the rear cross tube 36 of the frame 4 by a mount 50 and a pivot connection 52, about which the actuator assembly 32 may rotate when in operation. The actuator assembly 32 further comprises an actuation rod 54 extending forwards from the assembly, the free end of which is pivotably connected to the mount 44 on the upper portion of the headstock 14. Details of the actuator assembly 32 and its operation are set out below.

The headstock mount 12 is shown in more detail in Figure 3, which is a perspective view of the headstock mount of the frame of Figure 2. The headstock mount 12 comprises a generally rectangular rear member 60 having an upper portion 62 and a lower portion 64, with the lower portion being wider than the upper portion.

Each of the upper and lower portions 62, 64 comprise recesses 66 and 68 respectively, to receive transverse tubes of the frame 4. In particular, the recess 66 in the upper portion 62 is shaped to receive the front cross tube 34, as shown in Figure 2. The headstock mount 12 further comprises side walls 70 and 72, extending perpendicular to and forwards of the rear member 60, with the space between the side walls 70 and 72 being for receiving the headstock 14, again as shown in Figure 2. Each side wall 70 and 72 has a transverse bore 74 therethrough, for accepting the pivot shaft for mounting the headstock 14.

The headstock 14 is shown in more detail in Figure 4. The headstock 14 comprises a generally tubular portion 80, having a longitudinal bore 82 therethrough.

A transverse tubular portion 84 is disposed at the lower end of the tubular portion 80, through which extends a transverse bore 86 for accepting the pivot shaft for mounting the headstock 14 to the headstock mount 12. Side members 88 and 90 extend from the transverse tubular portion 84 along the length of the tubular portion and provide the mount 44 for connection to the actuation rod 54 of the actuator assembly 32.

Referring now to Figure 5, there is shown a plan view of the actuator assembly 32 in position in the frame 4 between the upper frame members 6. The actuator assembly 32 comprises a hydraulic actuator 100 of conventional arrangement connected to the actuation rod 54, whereby the actuator 100 is operable to move the actuation rod 54 longitudinally. The hydraulic actuator 100 is operated under the control of a servomechanism (servo) 102. Hydraulic fluid under pressure is retained in each of a pair of accumulators I 04a and I 04b, mounted longitudinally on opposite sides of the actuator 100. The accumulators 104a, 104b are fed with pressurized hydraulic fluid from a pump (not shown) driven by a suitable power transmission assembly from the engine, for example by a belt, chain or sprocket drive assembly from a suitable rotating shaft in the engine, in particular the crankshaft.

The actuator assembly 32 is operated under the control of a processor assembly (not shown for clarity). The processor may be located in any suitable position within the frame.

The actuator assembly 32 further comprises means for indicating the position of the actuator and, in turn, the angle of the headstock 14 and the steering assembly.

In particular, a sensor 106 is provided to determine the position of the actuator and provide a feed back signal to the microprocessor regarding the position of the actuator. The sensor 106 may be any suitable sensor, such as a linear potentiometer, available commercially and known in the art.

The actuator assembly 32 comprises one or more pressure transducers, each of which operatest to monitor the pressure of hydraulic fluid in the accumulators 1 04a and 104b. In operation, once the operating pressure of the fluid in the actuator assembly has been reached, the pressure transducers trigger a dump valve, which allows fluid from the pump to bypass the actuator assembly. This allows the pump to continue operation and circulate fluid off-load and allows the pump to remain able to supply fluid at pressure when required, while avoiding the pump overheating. The actuator further comprises safety valves (not shown for clarity), including a safety relief valves located at the rear of the actuator. In this way, should the vehicle be involved in a collision, any increase in fluid pressure at the rear of the actuator is relieved, reducing the risk of damage or injury.

Finally, the actuator assembly 32 includes one or more check valves, again not shown for clarity, which allow the actuator to be locked in position, should the operating pressure of the hydraulic system fall below a minimum threshold value. In this way, incorrect operation of the system due, for example to a leak in the hydraulic fluid supply system, is avoided.

As described above, the present invention operates to adjust or alter the angle of the steering assembly of the motorcycle in response to the angle of lean of the vehicle and its speed. Referring to Figure 6, there is shown a schematic representation of the control and activation system according to one embodiment of the present invention. As described hereinbefore and shown in Figure 6, the headatock 14 of the motorcycle is connected to the actuation rod 54 extending from the actuator 100, whereby the actuator is operable to rotate the headstock 14 about its pivot and change the angle of the steering assembly. The actuator is controlled by a servo 102, which in turn receives signals from a microprocessor 120.

The microprocessor 120 operates to receive and process the signals provided to it by a series of sensors and generates the appropriate signals for operation of the servo. In particular, the microprocessor 120 receives signals from an array of one or more lean angle sensors 122 and one or more speed sensors 124. As the angle of lean and/or the speed of the motorcycle changes during use, the microprocessor calculates the appropriate or optimum angle for the steering assembly, providing a signal to the servo to have the headstock 14 moved to the appropriate position. In addition, the microprocessor 120 receives feedback data from a linear potentiometer 126, indicating the position of the actuator and, hence, the current angle of the steering assembly.

Hydraulic fluid is provided under pressure to the servo from each of the two accumulators 1 04a,b. Fluid under pressure is supplied to each accumulator by a pump 130 from a fluid reservoir, for example the oil tank 132 shown in Figure 6.

Hydraulic fluid at low pressure from the servo 102 is returned to the tank 132 via the hydraulic fluid return line 134.

In operation, the microprocessor 120 receives signals from the lean angle sensor 122 and the speed sensor 124, together with a feedback signal from the linear potentiometer 126 regarding the position of the actuator mechanism. The microprocessor determines the appropriate angle for the headstock and steering assembly, based upon the lean angle of the motorcycle and its speed. The microprocessor then activates the servo 102 and actuator assembly 100 to change the angle of the headstock 14 as required to the appropriate angle. In this respect, for a motorcycle traveling at a high speed and initiating a turn, as the lean angle increases, the headstock is rotated to decrease the castor angle of the steering assembly. An increase in the angle of lean prompts the castor angle of the steering assembly to be further decreased. As the motorcycle exits the turn and the lean angle reduces as the vehicle moves to an upright position, the castor angle of the steering assembly is increased, to provide improved straight line stability.

The microprocessor 120 has a predetermined minimum speed, whereby the motorcycle must be traveling at or above this minimum speed, in order for the system to be activated and adjustments in the angle of the headstock and steering assembly made.

The system may be arranged with a maximum or rest' castor angle for the steering assembly, such that this angle is maintained while the motorcycle is at rest, traveling at a speed below the predetermined minimum or is traveling at higher speeds in a straight line (that is the vehicle is upright and the lean angle is zero).

The microprocessor and actuator act to reduce the castor angle when the motorcycle is leaned to one side when initiating a turn, the steering assembly being returned to the rest castor angle when the turn has been completed. In this arrangement, the rest castor angle is at one end of the range of adjustment of the castor angle.

Alternatively, the system may be arranged with the rest castor angle at a point within the range of adjustment. The castor angle is reduced from the rest angle when the motorcycle begins to turn and the lean angle increases. In addition, as the speed of the motorcycle increases in a straight line, the castor angle is increased by the microprocessor in response to the signal from the speed sensor.

Claims

1. A motorcycle comprising: a frame; a steering assembly connected to the frame and having an adjustable angle; means for adjusting the angle of the steering assembly; wherein the means for adjusting the angle of the steering assembly is operable in response to the angle of lean of the motorcycle.

2. The motorcycle according to claim I wherein the means for adjusting the angle of the steering assembly is operable to reduce the angle as the angle of lean of the motorcycle increases.

3 The motorcycle according to either of claim 1 or 2, wherein the angle of the steering assembly may be adjusted by up to 20 .

4. The motorcycle according to claim 3, wherein the angle of the steering assembly may be adjusted by up to 15 , more preferably up to 100, especially from 0 to 5 .

5. The motorcycle according to any preceding claim, wherein the steering assembly is connected to the front portion of the frame of the motorcycle by an adjustable mount, the means for adjusting the angle of the steering assembly acting on the adjustable mount.

6. The motorcycle according to claim 5, wherein the mount comprises a pivot, about which the steering assembly may be rotated.

7. The motorcycle according to claim 6, wherein the mount comprises a headstock pivotably connected to the frame, the steering assembly being connected to the headstock.

8. The motorcycle according to claim 7, wherein the headstock is pivotably connected below its mid point

9. The motorcycle according to claim 8, wherein the headstock is pivotably connected at its lower end portion.

10. The motorcycle according to any preceding claim, wherein the means for adjusting the angle of the steering assembly comprises an actuator.

11. The motorcycle according to claim 10, wherein the actuator is a hydraulic actuator.

12. The motorcycle according to claim 11, wherein the actuator is provided with hydraulic fluid from a plurality of accumulators.

13. The motorcycle according to any of claims 10 to 12, wherein the actuator is mounted to frame so as to provide a substantially horizontal force acting upon the steering assembly.

14. The motorcycle according to claim 13, wherein the actuator is mounted in the upper portion of the frame behind the connection between the steering assembly and the frame.

15. The motorcycle according to any of claims 10 to 14, wheretn the actuator is connected to the steering assembly through a pivotable connection.

16 The motorcycle according to any of claims 10 to 15, wherein the actuator is connected to the frame by a flexible or pivotable mount.

17. The motorcycle according to any preceding claim, wherein the means for adjusting the angle of the steering assembly is operable in response to the speed of the motorcycle.

18. The motorcycle according to claim 17, wherein the means for adjusting the angle of the steering assembly is operable only when the motorcycle is moving.

19. The motorcycle according to claim 18, wherein the said means is operable only when the motorcycle is moving at a speed above a predetermined minimum speed.

20. The motorcycle according to any preceding claim, wherein the means for adjusting the angle of the steering assembly comprises a processor.

21. The motorcycle according to any preceding claim, further comprising an override for the means for adjusting the angle of the steering assemb'y.

22. The motorcycle according to any preceding claim, wherein adjustment of the angle of the steering assembly results in the ground clearance of the motorcycle increasing as the angle is reduced.

23. A motorcycle comprising: a frame; a headstock pivotably mounted to the frame so as to be rotatable about the mount in a vertical plane; a steering assembly connected to the headstock; wherein the headstock is mounted to the frame at a position below the centre point of the headstock; and means for pivoting the headstock about its mount in response to one or more of the speed of the motorcycle and the lean angle of the motorcycle.

24. The motorcycle according to claim 23, wherein the headstock is mounted to the frame at its lower end region.

25. The motorcycle according to either of claims 23 or 24, further comprising means for rotating the headstock about the pivot, the said means being connected to the upper end portion of the headstock.

26. A frame for a motorcyde as defined in any preceding claim.

27. A headstock assembly for a motorcycle, the headstock assembly comprising a headstock mount adapted to be incorporated into the front portion of a motorcycle frame; and a headstock, the headstock being connected to the headstock mount so as to be pivotable about a point in the headstock below its centre point.

28. The headstock assembly according to claim 27, wherein the headstock is pivoted about its lower end portion. l0

29. A method of operating a motorcycle, the motorcycle comprising a steering assembly and means for adjusting the angle of the steering assembly, the method comprising.

monitoring the lean angle of the motorcycle; adjusting the angle of the steering assembly in response to changes in the lean angle of the motorcycle.

The method according to claim 29, wherein the angle of the steering assembly is adjusted only when the motorcycle is in motion.

31. The method according to either of claims 29 or 30, wherein the method further comprises monitoring the speed of the motorcycle and adjusting the angle of the steering assembly in response to both the speed and the lean angle.

32. The method according to any of claims 29 to 31, wherein the angle of the steering assembly is reduced as the lean angle of the motorcycle increases.

33 The method according to any of claims 29 to 32, wherein the angle of the steering assembly is increased as the speed of the motorcycle increases.

34. The method according to any of claims 29 to 33, wherein decreasing the angle of the steering assembly increases the ground clearance of the motorcycle.

35. A method of operating a motorcycle, the method comprising: with the motorcycle moving at a first speed, providing the vehicle with a first steering angle; with the the motorcycle moving at a second speed, greater than the first speed, providing the vehicle with a second steering angle, greater than the first steering angle; as the motorcycle is accelerated between the first and second speeds, adjusting the steering angle between the first angle and the second angle.

36. The method according to claim 35, wherein the first speed is zero.

37. The method according to either of claims 35 and 36, wherein the second speed is a threshold speed, above which no further increase in the steering angle takes place.

38. The method according to any of claims 35 to 37, wherein the first steering angle and second steering angle differ by an angle of from 0 up to 200, more preferably up to 15 .

39. The method according to any of claims 35 to 38, wherein the first angle is from about 15 to 25 , more preferably about 20 .

40. The method according to any of claims 35 to 39, wherein the second angle is from about 30 to 40 , more preferably about 350

41. A method of operating a motorcycle from a rest position, the method comprising: providing the motorcycle with a first angle for the steering assembly with the motorcycle at rest; accelerating the motorcycle; and reducing the angle of the steering assembly from the first angle as the motorcycle accelerates away from the rest position.

42. The method according to claim 41, wherein the first angle is from about 30 to about 40 , more preferably about 35 .

43 The method according to either of claims 41 or 41 wherein the reduction in the angle of the steering assembly is controfled by the operator of the motorcycle.

44. A motorcycle substantially as hereinbefore described having reference to the accompanying figures.

45. A frame for a motorcycle substantially as hereinbefore described having reference to the accompanying Figures 1 to 5. I0

46. A headstock assembly substantially as hereinbefore described having reference to the accompanying Figures 1, 2 4 and 5.

47. A method of operating a motorcycle substantially as hereinbefore described.

48. A method of operating a motorcycle from a rest position substantially as hereinbefore described.