WO2008065436A1

WO2008065436A1 - Suspension system

Info

Publication number: WO2008065436A1
Application number: PCT/GB2007/004630
Authority: WO
Inventors: Nicholas Richard Shotter
Original assignee: The Four Wheeled Motorcyle Company Ltd
Priority date: 2006-12-01
Filing date: 2007-12-03
Publication date: 2008-06-05
Also published as: EP2099624A1

Abstract

A suspension system for a leanable vehicle having a pair of laterally spaced wheels (1, 2) with hydraulic dampers (17, 18) associated with the wheels and control means selectively operable to operate a changeover valve (25) to cause the dampers (17, 18) to operate either independently or simultaneously to alter the operating characteristics of the suspension. In one position of a changeover valve (25), chambers above and below pistons (17b and 18b) are interconnected for each damper to allow normal tilting of the vehicle while still permitting suspension movements. In a second position of the changeover valve (25), the chamber above piston (17b) is interconnected with the chamber below piston (18b) and the chamber below piston (17b) is interconnected with the chamber above piston (18b), thereby preventing further tilting of the vehicle, whilst maintaining full suspension movement.

Description

Suspension System

This invention relates to a suspension system for a pair of laterally spaced wheels of a leanable vehicle. Particular embodiments of the invention relate to a suspension system for motorcycle-type vehicles having a pair of laterally spaced wheels, such as narrow tracked, leanable, four wheeled motorcycle type vehicles of the type disclosed in European patent application Nos. EP01998472.3 and EP03253106.3.

European patent application no. EP03253106.3, discloses a suspension system for a leanable vehicle in which separate dampers may be provided for a pair of suspension swing arms. The dampers can be connected to a valve which can be actuated to shut off the flow of hydraulic fluid through the dampers to prevent all movement of the suspension assembly relative to the vehicle, thereby preventing the vehicle from leaning further than desired. Resilient blocks may be provided between the dampers and their respective mounting points on the vehicle to offer some residual suspension movement when the dampers are locked.

The invention provides a suspension system for a leanable vehicle having a pair of laterally spaced wheels with dampers associated with the wheels and control means selectively operable to cause the dampers to operate either independently or simultaneously to alter the operating characteristics of the suspension.

This arrangement ensures that full movement of the suspension relative to the vehicle is maintained. This diminishes the need for additional components such as resilient blocks to provide residual suspension when the suspension system is used to limit the angle to which the leanable vehicle can lean.

A preferred embodiment of the present invention will be described, by way of example with reference to the attached figures. In the figures:

Figure 1 is a schematic illustration of a suspension system of the present invention for a leanable vehicle having a pair of laterally spaced wheels;

Figure 2 is a schematic illustration of the suspension system of Figure 1 when both wheels simultaneously traverse the same sized bump;

Figure 3 is a schematic illustration of the suspension system of Figure 1 when only one wheel traverses a bump;

Figure 4 is a schematic illustration of the suspension system of Figure 1 when the leanable vehicle leans in one direction, for instance, during cornering;

Figure 5 is a schematic illustration of the suspension system of Figure 1 when the leanable vehicle leans in an opposite direction to that shown in Figure 4;

Figure 6 is a schematic illustration of the suspension system of Figure 4 when both wheels of the leanable vehicle simultaneously traverse the same sized bump;

Figure 7 is a schematic illustration of the suspension system of Figure 5 when both wheels of the leanable vehicle simultaneously traverses the same sized bump;

Figure 8 is a schematic illustration of a part of the suspension system of Figure 1 when a pair of dampers of the system are configured to provide independent suspension using a rotary type valve;

Figure 9 is a schematic illustration of a part of the suspension system of Figure 1 when a pair of dampers of the system are configured to provide simultaneous suspension using a rotary type valve; Figure 10 is a schematic illustration of a part of the suspension system of Figure 1 when a pair of dampers of the system are configured to provide independent suspension using a linear type valve;

Figure 11 is a schematic illustration of a part of the suspension system of Figure 1 when a pair of dampers of the system are configured to provide simultaneous suspension using a linear type of valve;

Figure 12 is a schematic illustration of a first type of control system for the suspension system of the invention as shown in Figure 1 ;

Figure 13 is a schematic illustration of a second type of control system for the suspension system of the invention as shown in Figure 1.

Figure 14 is a schematic illustration of elements of the control system of Figure 13 integrated into the suspension system of Figure 8;

Figure 15 is a schematic illustration of elements of the control system of Figure 13 integrated into the suspension system of Figure 9.

Figure 16 is a schematic illustration of the suspension system of Figure 1 in which the suspension dampers are pneumatically operated;

Figure 17 is a schematic illustration of a part of the suspension system of Figure 16 showing the pneumatic suspension dampers connected to a changeover valve.

Figure 1 shows a rear suspension arrangement for a leanable vehicle having a pair of ground engaging wheels 1 and 2, mounted to the free ends of swing arms 3 and 4 respectively via stub axles (not shown). An opposite end of each of swing arm 3 and 4 is coupled to the vehicle so that swing arms 3 and 4 pivot about an axis that is substantially parallel to the rotational axis of ground engaging wheels 1 and 2. A connecting rod 6 is connected at one end to swing arm 3 at a swivel joint 8 and at its other end to one arm of a balance beam 5 at a swivel joint 9. Connecting rod 7 connects an opposite arm of balance beam 5 to a free end of swing arm 4, at swivel joints 10 and 11. Balance beam 5 can rotate about pivot 12 which is coupled to a cross head 13 of the leanable vehicle. Cross head 13 can slide along a pair of static guide rods 14 and 15 which are anchored at each of their ends (not shown) to the vehicle. One end of a suspension spring 16 is coupled to cross head 13. An opposite end of suspension spring 16 is coupled to an anchor point (not shown) on the vehicle.

Hydraulic dampers 17 and 18 are coupled between the balance beam 5 and mounting points (not shown) on the vehicle. Specifically, a piston rod 17a of hydraulic damper 17 is pivoted at one end to balance beam 5 at a swivel joint 19 (which in Figures lies behind, and is therefore obscured by, swivel joint 9), and damper housing 17d is coupled to a mounting point (not shown) on the vehicle. A piston rod 18a of hydraulic damper 18 is pivoted at one end to balance beam 5 at swivel joint 20 (lies behind swivel joint 11 , hence also obscured from the Figures), and damper housing 18d is coupled to a mounting point (not shown) on the vehicle. The swivel joints 19 and 20 are not restricted to being aligned with swivel joints 9 and 11 but are shown this way in the Figures for simplicity.

Referring to Figure 2, when ground engaging wheels 1 and 2 simultaneously traverse the same sized bump, the upward motion of the wheels causes the free ends of swing arms 3 and 4, to which the stub axles and wheels are attached, to rotate about their pivots (not shown). Simultaneously, connecting rods 6 and 7 cause the balance beam 5 and cross head 13 assembly to slide along static guide rods 14 and 15. This upward movement of the crosshead 13 and balance beam 5 assembly compresses spring 16 between cross head 13 and the upper anchor point (not shown) of the spring and causes piston rods 17a and 18a (see Figure 8) to push pistons 17b and 18b up through damper housings 17d and 18d of hydraulic dampers 17 and 18 (see Figure 8). Dampers 17 and 18 provide a damping effect to damp out unwanted oscillations of spring 16.

Balance beam 5 ensures that an equal force is exerted by suspension spring 16 through the cross head 13, pivot 12, balance beam 5 and swing arms 3 and 4 onto each of ground engaging wheels 1 and 2.

In the event that, for instance, ground engaging wheel 1 traverses a bump while the other remains stationary in a vertical direction (see Figure 3), the upward motion of, ground engaging wheel 1 compresses suspension spring 16 through movement of the swing arm 3, connecting rod 6, balance beam 5 and cross head 13. As wheel 1 rises, balance beam 5 rotates about pivot 12. Balance beam 5 applies an upward force to piston rod 17a through swivel joint 19, which forces piston 17b upwards through damper 17.

Figures 2 and 3 represent different suspension conditions in which both wheels simultaneously encounter the same sized bump (Figure 2) or only one wheel encounters a bump (Figure 3). In either case the suspension arrangement ensures that the spring force is substantially equally distributed between the two ground engaging wheels 1 and 2. This is also the case when the wheels are on flat ground or traversing different sized bumps or troughs. Rotation of balance beam 5 about pivot 12 ensures that a substantially equal force is exerted by suspension spring 16 through the cross head 13, pivot 12, balance beam 5 and connecting rods 6 and 7 on each of the ground engaging wheels 1 and 2.

Figures 4 and 5 show the suspension system configuration as the vehicle is leaned over in one direction (Figure 4) or the opposite direction (Figure 5) to, for instance, enable the rider to turn the vehicle around bend. Referring to Figure 4, as the vehicle leans into a bend, an inside wheel 2 rises and an outside wheel 1 falls, causing balance beam 5 to rotate about pivot 12. Simultaneously, piston rods 17a and 18a force pistons 17b and 18b (see Figure 8) in opposing directions through dampers 17 and 18 respectively. When the vehicle leans in the opposite direction (Figure 5), the suspension adopts the opposite configuration to that previously described for Figure 4.

Under normal, stable handling conditions, the vehicle and rider combination remains substantially balanced under the action of gravity when the vehicle is travelling in a straight line, or due to the resultant force acting on the vehicle which results from the combination of the gravitational and centrifugal forces generated by the vehicle as it travels around a bend. In the event that the forces influencing the vehicle cause it to become unbalanced, these unbalanced forces act as a lever acting around the wheels which act as a fulcrum, and the vehicle will be pulled down to the ground.

When the vehicle experiences such an unbalancing event of this kind, it is possible to prevent the vehicle from falling down by limiting the rotation of balance beam 5 about pivot 12. Embodiments of the invention provide a means for selectively preventing balance beam 5 from rotating about pivot 12 whenever necessary or desired, whilst enabling the vehicle to maintain full suspension movement.

In the preferred embodiment, balance beam 5 is prevented from rotating by the provision of a valve assembly to redirect the flow of hydraulic fluid through dampers 17 and 18. This is descried in more detail below.

During stable handling of the vehicle (shown in Figures 2 to 7), each wheel 1 and 2 is movable relative to the vehicle, independently of the movement of the other wheel. This is because a separate hydraulic flow circuit (Figure 8) is associated with each of the dampers 17 and 18. Therefore, the wheels can rise and fall independently of each other. This arrangement enables one wheel to traverse a bump or fall into a trough or hole without substantially affecting the other wheel, or the wheels to traverse bumps or troughs of different dimensions without substantially affecting each other. When a separate hydraulic flow circuit is provided for each damper, the suspension system is operating in an independent suspension mode, which is described in detail below.

In order to prevent the lateral acceleration experienced by the vehicle during an unbalancing event of the type previously described from causing an accident, the separate hydraulic flow circuits associated with dampers 17 and 18 are interconnected (Figure 9). In this configuration, movement of piston 17b in one direction through damper housing 17d will simultaneously cause movement of piston 18b through damper housing 18d in the same direction as piston 17b and vice versa. The wheels are no longer movable independently of each other and movement of one wheel becomes dependent on movement of the other wheel. In this case, the suspension system is operating in a simultaneous suspension mode, which is described in detail below.

When operating in the simultaneous mode, the vehicle still benefits from full suspension movement as provided by spring 16 and dampers 17 and 18, without substantially affecting the vehicle's lateral angle relative to the ground.

The suspension system can be switched between the independent mode and the simultaneous mode using manual and/or automatic actuation which is described in more detail below.

The independent and simultaneous suspension operating modes are shown in Figures 8 and 9 respectively. Referring to Figure 8, hydraulic damper 17 contains a two-way piston 17b coupled to piston rod 17a. A damper block 17c is coupled to the inside of damper housing 17d. Similarly, hydraulic damper 18 contains a two-way piston 18b and a damper block 18c. Pistons 17b and 18b have equal surface areas.

A suitable apparatus (not shown) would be coupled to each of damper blocks 17c and 18c to damp out unwanted oscillations of the spring 16.

Alternatively, the damper blocks 17c and 18c could be located externally to their respective damper housings 17d and 18d, in the hydraulic flow circuit associated with each damper.

Seals (not shown) are provided between the piston rods 17a and 18a and damper housings 17d and 18d respectively to prevent hydraulic fluid from leaking from the holes in the damper housings 17d and 18d which receive piston rods 17a and 18a respectively. Pistons 17b and 18b have seals (not shown) so that pistons 17b and 18b have a sealing fit inside their respective damper housings, which substantially prevents hydraulic fluid form escaping around the pistons as they move in either direction relative to an inside surface of their respective damper housing 17d,18d.

An orifice 21 at one end of damper housing 17d is connected to an orifice 22 at an opposite end of damper housing 17d by hydraulic lines 23 and 24 which are interconnected at a changeover valve 25. Similarly, an orifice 26 at one end of damper housing 18d is connected to an orifice 27 at an opposite end of damper housing 18d by hydraulic lines 28 and 29 which are also interconnected at changeover valve 25. This arrangement substantially forms two independent hydraulic flow circuits, as indicated by the two different ohαdod αroao and flow arrows of Figure 8, each circuit interconnecting the chambers above and below the respective piston.

When, for example, the ground engaging wheel 1 traverses a bump, a force is applied through the swing arm 3 and balance beam 5 assembly described above to piston rod 17a which moves piston 17b in the direction marked 'A' (see Figure 8). This movement forces hydraulic fluid from above piston 17b through damper block 17c in the direction indicated by the hydraulic flow arrows (see Figure 8). Hydraulic fluid from above piston 17b is forced out of orifice 21 in damper housing 17d, along hydraulic line 23, through changeover valve 25, through hydraulic line 24 and into the housing 17d at orifice 22 to a position below piston 17b.

If the ground engaging wheel 1 instead drops into a groove or hole in the ground surface (e.g. a pothole) the suspension assembly will force piston rod 17a in the opposite direction to that marked 'A' (see Figure 8) and the hydraulic damper fluid will flow in the opposite direction to the flow arrows shown in Figure 8.

When ground engaging wheel 2 traverses a bump, a force is applied to piston rod 18a in the direction of arrow 'B', which causes piston 18b to force hydraulic fluid from above piston 18b through damper block 18c, out of orifice 26, through hydraulic line 28, changeover valve 25 and hydraulic line 29 and through orifice 27 to a position below piston 18b. As described for the hydraulic system associated with damper 17, if ground engaging wheel 2 instead falls into a hole or trough, the hydraulic fluid will flow in the opposite direction to that indicated by the flow arrows (see Figure 8) and hydraulic fluid will flow from a position below piston 18b to a position above it.

As ground engaging wheels 1 and 2 rise and fall in response to undulations in the ground surface, the provision of a separate hydraulic flow circuit for each of dampers 17 and 18 enables the wheels to move independently as they travel across the ground surface.

In an alternative embodiment, hydraulic dampers 17 and 18 could be connected between the swing arms 3 and 4 respectively and the arm of balance beam 5 to which they are respectively connected. Alternatively, the piston rods 17a and 18a could be coupled at each end to the vehicle chassis with their respective clamper housings 17d and 18d being connected to the balance beam 5.

In another alternative embodiment, pistons 17b and 18b could have different surface areas. This arrangement could suit a non-symmetrical suspension arrangement of the type previously described to allow, for instance, the suspension system components to be located on the vehicle around other components of the vehicle whose location is more rigidly determined by the structure of the vehicle. For example, balance beam 5 could have an offset pivot 12 (so that one arm of the balance beam is longer than the other arm) and/or connecting rods 6 and 7 could be coupled to their respective swing arms 3 and 4 at different distances from the axis of rotation of the swing arms. Also, the suspension system could itself be symmetrical but offset in relation to the longitudinal centre line of the vehicle.

Figure 9 shows the suspension system of the invention in its simultaneous mode. This is achieved by rotating a valve member 30 of a rotary valve 25 about a pivot 31 to the position shown in Figure 9. With valve member 30 in this position, damper housings 17d and 18d are interconnected via hydraulic lines 23, 24, 28 and 29 as shown by the hydraulic flow arrows in Figure 9.

In simultaneous suspension mode, as ground engaging wheel 1 rises as it traverses a bump, the suspension system causes piston rod 17a to move in the direction marked 'A'. Piston 17b attached to piston rod 17a forces hydraulic fluid through damper block 17c, out of orifice 21, through hydraulic line 23, changeover valve 25, hydraulic line 29 and orifice 27 to a position beneath piston 18b. This hydraulic flow causes piston 18b to move simultaneously upwards through damper housing 18d in direction 'B', which forces hydraulic fluid from above piston 18b, through damper block 18c, orifice 26, hydraulic line 28, changeover valve 25, hydraulic line 24 and orifice 22 to a position beneath piston 17b. If ground engaging wheel 1 drops into to a trough or hole in the ground, the hydraulic fluid flows in the opposite direction to that described above i.e. in the opposite direction to that shown by the flow arrows in Figure 9. This results in a corresponding downward force being applied to ground engaging wheel 2. Similarly, if ground engaging wheel 2 drops into a trough or hole, a corresponding downward force will be applied to ground engaging wheel 1.

The position of valve member 30 can be changed to select the suspension operating mode using manual and/or automatic actuation means as described below in more detail.

The valve member 30 could also have an intermediate position between the positions shown in Figures 8 and 9, wherein the suspension system is in an intermediate operating mode. In this mode, the changeover valve 25 could substantially eliminate all flow of hydraulic fluid through the valve 25. This would have the effect of substantially eliminating all movement of the suspension system by using the dampers as a locking means to prevent the rotational movement of the balance beam 5 and sliding movement of cross head 13 assembly relative to the vehicle.

The vehicle may be parked with either the simultaneous or intermediate operating mode selected, to prevent the vehicle from leaning. Also, in either of these modes, the vehicle may be forceably leaned over as require so that a wheel is lifted from the ground to a suitable position for it to be changed. When transporting the vehicle, the intermediate mode is advantageously selected so that only the wheels and not the vehicle body require strapping down to prevent the vehicle from moving around. Also, the sprung mass of the vehicle is prevented from extending and compressing the suspension system as the vehicle is transported.

In another embodiment as shown in Figures 10 and 11 , the changeover valve 25 is a linearly operated valve 32 shown as a simplified spool valve having valve housing 33 and a spool with flow diverters 34,35,36 coupled to a shaft 37. The spaces around the shaft and between adjacent pairs 34,35 and 35,36 of flow diverters define annuli 38 and 39.

A hydraulic connection (not shown) interconnects each end of housing 33 to ensure that the hydraulic forces acting on the spool are balanced so that the control means can move the spool rapidly and with a relatively low force.

When the spool is in the independent mode position shown in Figure 10, hydraulic flow lines 23, 24, 26 and 29 all interconnect at annulus 38. When a force is applied to piston rod 17a in the direction marked 'A', hydraulic fluid is forced by piston 17b, through the damper block 17c, out or housing 17d, along hydraulic line 23, through annulus 38, along hydraulic line 24 and back into damper housing 17d to the underside of piston 17b, as shown by the flow arrows. A force applied in direction ¹B' pushes hydraulic fluid through the flow circuit associated with damper 18 in the same fashion as that described for damper 17.

When the spool is moved to the simultaneous suspension position shown in Figure 11, hydraulic flow lines 23 and 29 interconnect at annulus 38 and flow lines 26 and 24 interconnect at annulus 39. The damper chamber above each piston is therefore interconnected with the damper chamber below the other piston. When a force is applied to piston rod 17a in, for example, the direction marked 'A' hydraulic fluid is forced by piston 17b along hydraulic lines 23 and 29 and into damper 18. Simultaneously, piston 18b with attached piston rod 18a forces hydraulic fluid along hydraulic lines 26 and 24 into damper 17. The direction of movement and the distance travelled by each piston and piston rod assembly is therefore substantially equal.

Figure 12 shows a control system for controlling the operating mode of the suspension system embodying the invention. Accelerometer 40 is connected to an actuator 41 by a connector 42. A manual device 43 is also connected to actuator 41 by a connector 44. Actuator 41 is connected to changeover valve 25 by a connector 45. A manual device 46 is also connected to changeover valve 25 by a connector 47.

Accelerometer 40 measures the lateral acceleration of a vehicle to which the suspension system is fitted. When accelerometer 40 detects abnormal lateral movement of the vehicle, for example, that the lateral acceleration of the vehicle has reached a threshold value at which the vehicle is approaching an unstable attitude, accelerometer 40 signals actuator 41 to change the position of the changeover valve 25. This switches the suspension system from independent to simultaneous mode and prevents further leaning of the vehicle. Abnormal lateral movement could be detected where the lateral acceleration of the vehicle is greater than the lateral acceleration normally experienced by the vehicle during stable operation as it leans to negotiate a bend.

When required, manual actuation device 43 can cause actuator 41 to move changeover valve 25 to change the suspension setting to simultaneous mode. Manual actuation device 43 can also be used to return the suspension system to independent mode.

Changeover valve 25 can also be operated directly by operation of manual changeover device 46. This has the effect of directly manually changing the suspension mode from independent mode to simultaneous mode, without the use of the actuator 41.

For improved safety, the system could be configured so that outputs from manual actuation device 43 and manual changeover device 46 cancel or interrupt and override signals received from other parts of the automatic actuation system. Furthermore, when manual means 43 and/or 46 are operated, the valve member of the changeover valve 25 could remain in the independent, simultaneous or intermediate position (in which the suspension is fully locked), without the use of sustained manual or powered assistance.

Actuator 41 could use mechanical, electrical, pneumatic or hydraulic means to change the position of the changeover valve between the independent, simultaneous and intermediate suspension mode positions.

The actuator 41 could use mechanical, electrical, pneumatic or hydraulic means both to change the suspension mode from independent mode to simultaneous mode when the defined lateral acceleration reaches the threshold value, and to return the suspension mode from simultaneous mode to independent mode when the lateral acceleration drops below the threshold value, or when the system receives a manual input, or after a programmed time delay.

Alternatively, a biasing means (not shown) could be provided which returns the changeover valve from the simultaneous to the independent mode position.

Where the actuator 41 is pneumatically actuated, the pressurised air required to drive the actuator could be tapped off from the crankcase of the engine of the vehicle to which the suspension system of the invention is fitted.

Alternatively, the pressurised air could be provided directly from a compressor or from a tank or other reservoir of pressurised air connected to, and filled by, a compressor. The compressor could be driven mechanically by the vehicle's engine or electrically by the vehicle's electrical system.

In another alternative, an integral drilling and/or bleed-off pipe could be used to fill a pressurised tank directly from the engine's combustion chamber, exhaust port or crankcase. An advantage of this arrangement is that the high pressure generated in the combustion chamber would mean that only a small pressurised tank would be required.

In a further alternative, a pneumatic actuator 41 could be actuated using a vacuum from a reservoir in which a vacuum is generated by a bleed-off from the engine at a point upstream of the combustion chamber. The vacuum could instead be generated by an evacuation valve connected to a vacuum reservoir or to the engine crankcase, whereby the engine crankcase would also function as a vacuum reservoir.

A valve could be positioned between the pressurised tank or vacuum reservoir and the pneumatic actuator. When opened by electrical, mechanical, pneumatic or hydraulic means, this valve would allow the pressurised air or vacuum to operate the pneumatic actuator which in turn operates the changeover valve.

A one-way valve could be positioned upstream of the pressurised tank or vacuum tank to prevent uncontrolled loss of either the pressurised air or the vacuum. Also, where a pressurised tank is used, a pressure release valve would be provided for safety to ensure that the pressure limit of the tank would not be exceeded.

Manual devices 43 and 46 could be operated by a suitable lever, button or knob as required. Connectors 42 and 44 could be electrical, mechanical, pneumatic or hydraulic as required by the actuator 41. Connector 47 could provide a mechanical connection with the changeover valve 25 which may be electrically, pneumatically or hydraulically assisted.

Preferably, connector 45 would provide a mechanical connection between the actuator 41 and changeover valve 25.

Figure 13 shows an alternative control system for the suspension system embodying the invention. In addition to the control system components and operation previously described, hydraulic flow sensors 48 and 49 are positioned in the hydraulic flow circuits associated with dampers 17 and 18 respectively (see also Figures 14 and 15) and detect the direction and/or rate of the flow of hydraulic fluid through the hydraulic flow circuits.

Connectors 50 and 51 connect a control unit 52 to sensors 48 and 49 (see also Figures 14 and 15). When control unit 52 detects from sensors 48 and 49 substantially equal hydraulic fluid flow rates in opposite directions through the hydraulic flow circuits associated with dampers 17 and 18 and/or a certain fluid flow rate past the sensors (both conditions indicating a high rate of vehicle lean experienced when the vehicle becomes unbalanced), control unit 52 connected to actuator 41 by a connector 53, causes actuator 41 to move changeover valve 25 from the independent to the simultaneous suspension mode. Connectors 50, 51 and 53 could be electrical, mechanical, hydraulic or pneumatic.

A manual controller 54 is connected to control unit 52 by a connector 55. This manual input can be operated by the rider to signal actuator 41 to activate changeover valve 25. A signal received from manual controller 54 could cancel or override signals received from components of the automatic control system.

The control unit 52 could be programmed as required to cause the actuator 41 to actuate the changeover valve 25 in response to one or more of substantially equal, disproportionate or dissimilar fluid flow characteristics experienced by flow sensors 48 and 49. The values at which the control unit will operate the changeover valve could be pre-set or manually adjustable by the rider, or could be varied in response to historic or real-time data relayed from the hydraulic flow sensors 48 and 49 and any other suitable sources. For example, vehicle speed and/or lateral movement data could be used to influence the operation of the control system. Another embodiment of the control system could incorporate a timer so that as the vehicle is unbalanced, the changeover valve 25 is switched to the simultaneous suspension mode position for a pre set, manually adjustable or automatically variable time period.

In an alternative embodiment of the suspension system, pneumatic damping devices may be provided. Figure 16 shows four pneumatic devices 101 , 102, 103, 104 connected at one end to balance beam 5 at swivel joints 120 and 121 and, at their other ends, to mounting points on the vehicle using swivel joints (not shown). Figure 17 shows pneumatic devices 101 , 102, 103, 104 connected by gas flow lines 105, 106, 107, 108 which are connected to a changeover valve 125.

The pneumatic devices could be Pneumatic Artificial Muscles (PAMs) in which a rubber or other resiliently deformable tube is sealed at each end to define an internal cavity, containing a valve at one or each end of the tube to selectively allow a gas (typically air) to pass into and out of the cavity. When the valve or valves allow pressurised air into the cavity, the resiliently deformable tube inflates, thereby contracting in length. When air is expelled from the cavity, the tube deflates whilst extending in length. An advantage of using PAMs is that as the tube is inflated and deflated, greater forces can be generated by the associated contractions and extensions for a given gas pressure than those produced by pneumatic piston and cylinder assembly of equal diameter.

In independent suspension operating mode, when wheel 1 moves in direction 'A', push rod 6 applies a force to the balance beam 5 which raises the arm of the balance beam to which swivel joint 120 is coupled. This extends pneumatic muscle 101 causing it to deflate, forcing gas through gas line 105, changeover valve 125 and gas line 106 into pneumatic muscle 102, causing it to inflate and therefore contract in length. A movement of wheel 1 in the opposite direction, stretches pneumatic muscle 102, displacing the gas into muscle 101 via gas line 106, changeover valve 125, and gas line 105. Similarly, movements of wheel 2 will cause the pneumatic muscles 103 and 104 to expand and contract as required, forcing the gas through gas lines 107 and 108 and changeover valve 125.

In simultaneous suspension operating mode, as wheel 1 moves in direction A, the arm of balance beam 5 to which swivel joint 120 is coupled rises, stretching pneumatic muscle 101. As pneumatic muscle 101 deflates, gas is displaced along gas line 105, changeover valve 125 and gas line 107 into pneumatic muscle 103. Simultaneously, pneumatic muscle 103 contracts in length, thereby extending muscle 104 to move wheel 2 in direction ¹B¹ and forcing gas through gas line 108, changeover valve 125 and gas line 106 into pneumatic muscle 102 which inflates and therefore contracts in length.

When wheel 1 moves in the opposite direction, the flow of gas is reversed. Similarly a force applied to wheel 2 to move it in a direction will force gas through the gas lines and changeover valve to move wheel 1 in the same direction.

Changeover valve 125 has the same function as the changeover valves used for the hydraulic damper system. The changeover valve 125 could therefore also have an intermediate position for locking the movement of the suspension and the degree to which the suspension system is locked could be varied by controlling the pressure of the gas contained within the PAMs and the pneumatic supply system.

Damping control could be achieved by controlling the valves which may be coupled to the pneumatic muscles directly or located in the gas flow lines which interconnect the pneumatic muscles. A Pneumatic Artificial Muscle of the construction and operation previously described could also be used to change the position of the changeover valve to select the required operating mode of the suspension system.

The suspension system previously described may also be fitted to the front of a leanable vehicle. Separate control systems of the types previously described could be provided for controlling the suspension characteristics of the front and rear suspension. Alternatively, a front suspension changeover valve and a rear suspension changeover valve could be simultaneously or individually activated by a single control system including a single control unit 52, accelerometer 40, actuator 41 , manual activation device 43, manual changeover device 46 and manual controller

54.

Where the suspension system of embodiments of the invention is fitted to both the front and rear of a leanable vehicle, the front and rear suspension could be switched between the independent and simultaneous suspension modes simultaneously or individually as required. The specific operation of the front and rear suspension could be fully programmable using the control unit 52 of the control system.

Some advantages of the suspension system of the present invention are that:

1. the independent suspension movement of each wheel can be changed to simultaneous suspension movement of a pair of wheels;

2. all suspension movement of a pair of wheels can be prohibited;

3. advantages 1 & 2 are substantially achievable using existing vehicle components, which minimises vehicle production costs; 4. as a result of advantage 3, the addition to the unsprung mass of the vehicle is minimised which in turn minimises the effect on vehicle handling and performance etc.;

5. as a result of advantage 3, the addition to the overall mass of the vehicle is minimised which in turn minimises the effect on vehicle handling and performance etc.;

6. as a result of advantage 3, the space required to accommodate the suspension system is minimised.

7. Where Pneumatic Artificial Muscles (PAMs) are used, they are lightweight, therefore minimising both the unsprung weight and the overall weight of the vehicle, thereby enhancing the vehicle performance and handling etc.

8. When PAMs are used, no energy is required to overcome the frictional forces at a piston/cylinder interface before the suspension system can begin to operate.

Claims

1. A suspension system for a leanable vehicle having a pair of laterally spaced wheels (1 ,2) with dampers (17,18) associated with the wheels and control means selectively operable to cause the dampers (17,18) to operate either independently or simultaneously to alter the operating characteristics of the suspension.

2. A suspension system according to claim 1 , wherein each damper (17,18) is double-acting with first and second working fluid connections at opposite ends and the control means includes a changeover valve (25) which in. a first position interconnects the first (21 ,26) and second (22,27) working fluid connections of each damper (17,18) and in a second position connects the first working fluid connection (21) of one damper (17) to the second working fluid connection (27) of the other damper (18) and the second working fluid connection (22) of said one damper (17) to the first working fluid connection (26) of the said other damper (18).

3. A suspension system according to claim 2, wherein the changeover valve (25) has a third position in which the working fluid is prevented from passing through the valve.

4. A suspension system according to claim 3, wherein in the third position of the changeover valve (25) is intermediate the first and second positions.

5. A suspension system according to any of claims 2 to 4 and including a sensor or sensors (48,49) for detecting abnormal lateral movement of the vehicle when the valve is in the first position to cause the control means to change the valve (25) to the second position.

6. A suspension system according to claim 5 wherein the, or each, sensor is an accelerometer (40).

7. A suspension system according to any of claims 2 to 6 including flow-sensing means for detecting abnormal working fluid flow characteristics when the valve (25) is in the first position to cause the control means to change the valve (25) to the second position.

8. A suspension system according to claim 7 wherein the flow-sensing means detects the flow rate of the working fluid.

9. A suspension system according to claim 7 wherein the flow-sensing means detects the direction of flow of the working fluid.

10. A suspension system according to any of claims 2 to 9 wherein the changeover valve (25) is a rotary valve having a valve member (30) rotatable between a first position in which the first (21 ,26) and second 22,27) working fluid connections of each damper (17,18) are interconnected and a second position in which the first working fluid connection (21) of one damper (17) is connected to the second working fluid connection (27) of the other damper (18) and the second working fluid connection (22) of said one damper (17) is connected to the first working fluid (26) connection of the said other damper (18) .

11. A suspension system according to any of claims 2 to 9 wherein the changeover valve (25) is a linearly operated valve movable between a first position in which the first (21 ,26) and second (22,27) working fluid connections of each damper (17,18) are interconnected and a second position in which the first working fluid connection (21) of one damper (17) is connected to the second working fluid connection (27) of the other damper (18) and the second working fluid connection (22) of said one damper (17) is connected to the first working fluid connection (26) of the said other damper (18)

12. A suspension system according to claim 11 wherein the linearly operated valve is spool valve.

13. A suspension system according to any of claims 2 to 12 for each of a pair of front wheels and a pair of rear wheels of a leanable vehicle with dampers associated with each pair of wheels having a common control means coupled to a front suspension changeover valve and a rear suspension changeover valve selectively operable to cause the front dampers and/or the rear dampers to operate either independently or simultaneously.

14. A suspension system according to any of the preceding claims wherein the dampers are hydraulic dampers (17,18).

15. A suspension system according to any of claims 1 to 13 wherein the dampers are pneumatic dampers (101 ,102,103,104).

16. A suspension system according to claim 15 wherein the working fluid is air.