Suspension improvements for a quadricycle

Abstract

The present invention provides a suspension system (10); comprising: a chassis (20), a hub (30) for mounting a wheel (34) thereto, a suspension linkage (40) extending between and the hub (30) and the

Description

Field The present invention relates to suspension and chassis components. More particularly, the present invention relates to chassis and suspension components for an electrically assisted quadracycle for carrying cargo. Background To address environmental concerns over air-pollution and greenhouse gas emissions there is a demand for alternatives to conventional motorised combustion vehicles which can meet the needs of the supply chain. In urban centres in particular, cargo delivery needs are increasingly met by human powered cycles, with and without electrical assistance to augment the pedal power of the rider. The addition of electrical power increases the range and speed of such cycles whilst retaining their benefits; namely their lack of contribution to air pollution and potential to ease traffic congestion due to their small size relative to other road vehicles. The cargo capacity of a conventional electrically assisted bicycle, or e-bike, is limited however, due to the bicycle’s decreased handleability at higher loads. Electrically assisted quadracycles provide a solution to this problem, the stability provided by their four-wheel configuration allowing higher cargo loads to be carried safely. In a typical vehicle of this type, such as the ones disclosed in GB2584919B and EP3380393B1, the rider is positioned at the front of the vehicle between the two front wheels and cargo is loaded behind the rider between the two rear wheels. With electric assistance it is possible for a quadracycle to carry a substantial load. This can be as much as 350kg or more giving an all up mass of 550kg for a heavy quadracycle for carrying goods. Quadracycles for carrying cargo are still often partially powered by pedals. In many jurisdictions by regulation an electric assisted quadricycle must only be electrically assisted meaning that the rider must be inputting a torque in order for the electrical assistance to function. It is common for such vehicles to be used as multi drop vehicles with users who may also be referred to as riders or drivers working for long shifts. Therefore, rider comfort, rider entry and egress from the riding position and safety are all important factors. The market for riders of such vehicles is competitive and rider retention is important, thus quadricycles of this type must be easy and comfortable to handle and use. The load that can be carried by a cargo quadricycle that is by its nature a lightweight vehicle is substantial relative to the mass of the unladen vehicle. This means that there is a large change in the way the vehicle handles between laden and unladen states. In particular the manner in which a laden quadricycle can corner and stop is very different to a unladen vehicle. It is important that a rider takes into account these changes when riding to maintain the safety of the rider, the quadricycle and those around them. Some quadricycles have a suspension system which must also accommodate these dramatically differing loads whilst maintaining function and handling. As well as the quadricycle being able to handle the loads that it is capable of carrying the rider must also pilot the quadracycle in a manner that is appropriate for the load it is carrying. Due to the electrical assistance fitted to many of these quadricycles the user may not be aware of the increased load. This can lead to cornering too fast and not leaving sufficient distance to allow a laden quadricycle to come to a stop. Summary of Invention Aspects and / or embodiments seek to provide solutions to the aforementioned problems. According to a first aspect, there is provided a suspension system for a quadricycle having a first compressed position, a second ride height position, a third extended position and a wheel rate R. The suspension system, comprising a chassis having a front end and a rear end and a central vertical plane P extending longitudinally from the front end to the back end. The suspension system also comprises a hub having fixings for rotatably mounting a wheel thereto and a suspension linkage extending between the hub and the chassis and rotatably mounted to the chassis. The suspension system also comprises a ride height control means comprising a first portion connected to and moveable by the chassis or one of the hub and suspension linkage and a second portion connected to and movable by the other of the chassis or one of the hub (30) and suspension linkage, The suspension system further comprises a bump resilient element located between a first part of the first portion and the second portion and an extension resilient element located between a second part of the first portion and the second portion; wherein the bump resilient element is compressed when moving from the second ride height position toward the first compressed position; and the extension resilient element is compressed when moving from the second ride height position toward the third extended position. The suspension system with two resilient elements, a first compressed when the suspension moved into compression or a lower ride height and a second compressed when the suspension system is in extension allows control of the wheel and the chassis in both bump and in rebound or extension of the system. This improves ride quality, roll control of the vehicle and eases the job of the user when riding the quadricycle. Optionally, the suspension system has a first wheel rate R1 in the first compressed position, a second wheel rate in the second ride height position, and a third wheel rate R3 in the third extended position, wherein R3 is greater than R1. Advantageously, providing the quadricycle with good bump absorption and ride comfort as the lower wheel rate is in compression and active on a heavily loaded wheel and good roll control as the suspension system that is in extension, normally on the side of the quadricycle on the inside when the quadricycle is going around a corner is in the stiffer region of the travel of the suspension system. This prevents the inside lifting as far and reduces roll without compromising the bump absorption of the loaded side. The suspension system 10 also prevents the suspension hitting a hard stop at the end of droop or extension travel. Optionally, the suspension system has a first wheel rate R1 equal to the second wheel rate R2. This advantageously provides the lower wheel rate R1 throughout the compression travel of the suspension system. However, it will be understood that the transition between R1 and R3 may occur below or above the second ride height position 12. Optionally the bump resilient element of the suspension system has a spring rate KB and the extension resilient element has a spring rate KR so that KB >KR for a given deflection. The softer extension resilient element is able to provide the increased spring rate as the suspension system preloads the two resilient elements against each other so that in the third extension position both springs are active. This advantageously provides a seamless transition between different wheel rates or suspension stiffnesses. Optionally the bump resilient element of the suspension system has an open length LB, the extension resilient element has an open length LR and at the second ride height position the extension resilient element has length LR. Advantageously, at the second ride height position the extension resilient element is not active, therefore the suspension system will provide the softer wheel rate R1 from the second ride height position as it compresses. Optionally, the ride height control means includes a first compression platform and a first extension platform connected to and movable with the first compression platform. The second portion of the ride height control means may include a second compression platform and a second extension platform connected to and movable with the second compression platform. The first compression platform may face the second compression platform and the bump resilient element is located therebetween. The first extension platform may face the second extension platform and the extension resilient element is located therebetween. Optionally, the first compression platform, the bump resilient element, the second compression platform, the second extension platform, the extension resilient element, and the first extension platform are arranged in the given sequence in a linear coaxial stack having a length LS. Optionally, the second compression platform and the second extension platform comprise opposite sides of a unitary component. Advantageously, providing a compact ride height control means with the fewest components. Optionally, there is a distance D1 between the first compression platform and the second compression platform and a distance D2 between the second extension platform and the first extension platform and D1+D2<LB+LR. Thereby, advantageously preloading the bump resilient element against the extension resilient element when in the third extended position and therefore providing the higher wheel rate R3. Optionally, at the second ride height position, D2 is approximately equal to LR. At the second ride height position the compression resilient element is compressed due to the weight of the quadracycle. When D2 is equal to LR the extension resilient element will be compressed as the suspension system extends from the ride height position into droop providing the spring rate R3. Optionally, the first portion of the ride height control means includes a stack length adjustment means for controlling the distance between the first compression platform and the first extension platform and thus (D1+D2). Changing the stack length adjusts preload placed on the bump resilient element by the extension resilient element which allows the point at which the suspension system starts to compress the extension resilient element to be adjusted and thus the point the spring rate increases from R1 to R3. Optionally, the stack length adjustment means comprises a rod or a cylinder having a first end connected to one of the first compression platform or the first extension platform and a second end having a threaded portion for receiving an adjuster having a complementary thread and connected to the other of the first compression platform or the first extension platform in order to control the distance therebetween. Optionally, the linkage of the suspension system is connected to the chassis at a pivot mount having an axis of rotation A extending longitudinally relative to the chassis about which the linkage may rotate. Advantageously providing movement of the link without resistance or stiction in order for the movement of the wheel to be controlled by the ride height control means. Optionally, the stack and / or stack length adjustment means extends tangentially to the axis of rotation A. Therefore, the stack is loaded axially as the linkage rotates, this is particularly advantageous when the first portion is fixed to the linage. Optionally, the ride height control means includes one or more ride height adjustment spacers between the first compression platform and the second compression platform. Adjusting the stack length can change the ride height if a transition point between R1 and R3 is chosen at a suspension position more compressed than the second ride height position. The ride height position is also dependent on the load carried by the suspension. Therefore, ride height adjustment spacers are useful for adjusting the second ride height position to the desired hight. Optionally, the bump resilient member and the extension resilient member extend about the rod or circumferentially within the cylinder such as to be located thereby. Advantageously, preventing the resilient elements becoming displaced. Optionally, the bump resilient member and the extension resilient member comprise a coil spring, an elastomer or other suitable resilient material. Optionally, the link is a swing arm, fixed to the hub. Advantageously, providing a simple suspension system with minimal components whilst providing a geometry with increasing negative camber when in droop and decreasing negative camber when the suspension system is in extension or droop. Optionally, the pivot mount includes a resilient bush allowing compliance in the linkage about a vertically extending axis B. Vertical axis B preferably intersects Axis A and vertically extending means anything close to vertical i.e. within 20 degrees. Most preferably axis B is perpendicular to Axis A. It will be understood that the compliance provided by the resilient bush will not define the Axis B tightly and therefore Axis B may vary within the range given above depending on how the suspension system is loaded. Optionally, the linkage comprises a first link extending from the chassis in a lateral direction having a first end connected to the chassis at a point M and a second end connected to the hub. The linkage may also comprise a second link extending in a lateral direction from the chassis and having a first end connected to the chassis at a point T and a second end connected to the hub and or to the first link proximal the second end of the first link, wherein T is offset toward the front end or the rear end of the chassis relative to M and the second link includes a resilient portion for allowing extension and compression of the second link. The second link provides triangulation of the linkage allowing longitudinal loads placed on the linkage to be fed into the chassis as tension and compression loads instead of bending loads as is the case for a single link. The resilient portion maintains a controlled amount of forward and rearward movement in the hub and wheel to allow absorption of bumps improving the ride comfort for the rider, preventing damage to the cargo and reducing the peak loads seen by the suspension system. Optionally, the resilient portion of the second link comprises one or more elastomers between one or more platforms and the chassis. Optionally, the linkage extends laterally from the chassis perpendicular to the central plane P. Optionally, the first portion of the ride height control means is fixed to and moveable with the linkage and the second portion of the ride height control means is fixed to and moveable with the chassis. This allows the first and second portions to be integrated with the structure of the respective components to which they are fixed providing a lower part count fewer failure points and a lighter suspension system. Optionally, the hub includes a steering pivot about which the hub may rotate having a steering axis of rotation S inclined to the vertical in the direction of plane P at caster angle a, wherein in the unladen state a <0.5 degree and in the laden state a >1. The lower the caster angle a the lighter the steering effort and also the lower the maximum lateral force that can be generated by the tyre on the road. It is conventional wisdom for the skilled person in quadricycles to maintain low steering effort in all conditions for ease of operation. However, as discussed above this can lead to a lack of appreciation of a change in the capability of the quadricycle when laden. The increased caster angle a in the laden state increases steering effort for the rider informing them that the vehicle is laden and encouraging lower cornering speeds whilst having the bonus secondary effect of increasing the lateral load that may be generated by the front steering wheels. Optionally, the linkage includes one or more front linkages for connecting a plurality of front hubs to the chassis having a front ride height control means providing a front wheel rate RF and one or more rear linkages for connecting a plurality of rear hubs to the chassis having a rear ride height control means providing a rear wheel rate RR, wherein RF is greater than RR. Optionally, the suspension system may direct >90% and preferably >98% of the load from the cargo carrying space through the rear hubs. Optionally, the chassis includes a cargo carrying space having a centre of plan area V located vertically above the fixings of the rear hubs for passing the load from said cargo through the rear axle only. Thereby ensuring that the attitude of the quadricycle is changed by the addition of the load and the caster angle increased. This has the secondary beneficial effect that the rear axle and rear ride height control means carrying the load may have a wheel rate adapted for the cargo and the front axle may have a wheel rate adapted for the rider. According to a second aspect there is provided a suspension system for a quadricycle having a first compressed position, a second ride height position, a third extended position and a wheel rate R, comprising a chassis having a front end and a rear end and a central vertical plane P extending longitudinally from the front end to the back end. The suspension system also comprises a plurality of front hubs having fixings for rotatably mounting a wheel thereto, a steering pivot about which the hub may rotate having a steering axis of rotation S inclined to the vertical in the direction of plane P at caster angle a, and a plurality of rear hubs having fixings for rotatably mounting a wheel thereto. The suspension system further comprises a suspension linkage extending between each of the hubs and the chassis and rotatably mounted to the chassis, so that in the unladen state a <0.5 degree and in the laden state a >0.5 degree and preferably a >1. Optionally, the linkage includes one or more front linkages for connecting a plurality of front hubs to the chassis, having a front ride height control means providing a front wheel rate RF and one or more rear linkages for connecting a plurality of rear hubs to the chassis having a rear ride height control means providing a rear wheel rate RR, wherein RF is greater than RR. Optionally, the chassis includes a cargo carrying space having a centre of plan area V located vertically above the fixings of the rear hub for passing the load from said cargo through the rear hubs. According to a second aspect there is provided a quadricycle having a suspension system as described above. Brief Description of Drawings Embodiments will now be described, by way of example only and with reference to the accompanying drawings having like-reference numerals, in which: Figure 1 shows a quadricycle including a suspension system according to the current invention; Figure 2 shows a suspension system according to the current invention as fitted to the quadricycle of figure 1; Figure 3 shows a variation of the suspension system shown in figure 2 further including a second link; Figure 4 shows the suspension system of figure 4 from below; and Figure 5 shows a section view of the suspension system of figure 4 taken at line S also shown in figure 4; Figure 6 shows a ride height control means of the current invention at a free length when not installed or no preload is applied to the resilient elements of the ride height control system; Figure 7 shows the ride height control means of the current invention in a third extended position; Figure 8 shows the ride height control means of the current invention at the second ride height position; Figure 9 shows the ride height control means of the current invention in a substantially compressed position. Figure 10 shows a schematic side view of an unladen quadricycle equipped with a suspension system according to the current invention; Figure 11 shows a schematic side view of a laden quadricycle equipped with a suspension system according to the current invention; Figure 12 shows a schematic top view of a quadricycle equipped with a suspension system according to the current invention; and Figure 13 shows the wheel rate RR of the rear axel with varying load. Specific Description Referring to Figure 1; a first embodiment will now be described. Figure 1 shows a quadricycle 1 equipped with one or more suspension systems 10 according to the current invention. The quadracycle 1 shown is a cargo carrying electrically assisted quadricycle 1 However, the current invention could be used with any type of quadricycle 1 or tricycle. The suspension system 10 comprises a chassis 20, a hub 30 suitable for rotatably mounting a wheel 34 thereto and a suspension linkage 40 extending between the hub 30 and the chassis 10. The suspension linkage 40 is rotatably mounted to the chassis 20. The chassis 20 has a front end 22 and a rear end 24 and a central vertical plane P extending longitudinally from said front end 22 to said back end 24. The hub 30 includes fixings 32 for mounting a wheel 34 thereto. The suspension system 10 is for suspending one wheel 34 of a quadricycle 1 but may be adapted to suspend two wheels 34 on the same axel. The quadricycle 1 has a plurality of the suspension systems 10 fitted. The suspension system 10 is particularly suited to suspending the quadracycle 1 at the front wheels 34f. However, it will be under stood that the suspension system can be used at any wheel 34 of a quadricycle 1. The suspension system 1 has a first compressed position 11 when the wheel is moved up in bump and the chassis 2 of the quadricycle 1 is moved down, a second ride height position 12 when the quadricycle 1 is at rest sat suspended on the suspension system 10 and a third extended position 13 when the wheel 34 is moved down in droop to a rebound position and the chassis 20 is moved up. Figure 2 shows a suspension system 10 for one wheel of a quadricycle 1. It can be seen in figure 2 the suspension linkage 40 rotatably mounted to the chassis 20 at a pivot mount 26. The pivot mount 26 has an axis of rotation A extending longitudinally from the front end 22 to the back end 24 relative to the chassis 20. The suspension system 10 further includes a ride height control means 60 for controlling the height of the chassis 10 above the ground and the articulation or movement of each hub 30 and therefore each respective wheel 34 relative to the chassis 20. The suspension system 10 includes a wheel rate R. The wheel rate R is the value of the stiffness or rate of the suspension; specifically (in ISO units) the force or load (in N) required to move the wheel relative to the chassis 20 by a distance (of one millimetre). The wheel rate R is controlled by the ride height control means 60 which is described in more detail with reference to figure 5 below. Note the wheel rate R is the effect of the stiffness of the ride height control means 60 at the hub 30 or wheel 34 taking in to account any mechanical advantage created by the linkage 40. In the embodiment of figure 2 the linkage 40 comprises a swing arm 40a. That swing arm 40a fixed to the hub 30 and movable therewith. The swing arm 40a extends laterally from the chassis 20 and may be perpendicular to the central plane P of the chassis 20, in particular when the linkage 40 comprises only a first link 41 such as a swing arm 40a. The suspension system 10 preferably has a first wheel rate R1 in the first compressed position 11 a second wheel rate R2 in the second ride height position 12 and a third wheel rate R3 in the third extended position 13. In a suspension system 10 of the current invention R3 is greater than R1. R2 may be the same as R1 or the same as R3 or may be between R1 and R3. Therefore, the quadricycle will move less as load is reduced on the wheel when in the third extended position 13. The increased wheel rate R3 is the result of the bump resilient element 62 and the extension resilient element 64 both being compressed at the same time and acting against one another in the ride height control means 60 as discussed further below. It is noted that in the embodiments shown in the figures that the resilient elements 62, 64 are both employed in compression, it will be understood that one or more of the resilient elements 62, 64 could be employed in extension within the scope of the current invention. Figures 3 and 4 show a variation on the suspension system 10 shown in figure 1. The linkage 40 may comprise a first link 41 extending from the chassis 20 in a lateral direction away from the central plane P. The first link 41 includes a first end 41 ib and a second end 41 ob. The first link 41 is rotatably connected to the chassis 20 at the first end 41 ib at pivot connection 26 and is rotatably about Axis A. The second end 41 ob is connected to the hub 30. The second end 41 ob may be fixed to the hub as shown in the figures or in the case of a more complex multilink arrangement (not shown) that provides sufficient constraint to the movement of the hub 30 the link 41 may be pivotally connected to the hub 30. Optionally, and included in the variation of figures 3 and 4, the linkage 40 may further comprise a second link 42 having a first end 42ib connected to the chassis 20 and a second end 42ob connected to the hub 30 and / or the first link 41. Preferably the second end 42ob is connected to the first link at or proximal the second end 41 ob of the first link. The second link 42 provides a fore aft support and / or control of the first link 41 and thus the hub 30 and wheel 34. The first end 41 ib of the first link 41 is connected to the chassis 20 at a point M and the first end 42ib of the second link 42 is connected to the chassis 20 at a point T. Point T is offset longitudinally toward the front end 22 or rear end 24 of the chassis 20 relative to point M in order to provide triangulation and transmit longitudinal loads from the wheel 34 and hub 30 into the chassis 20. The second link 42 preferably includes a resilient portion 44 for allowing extension and compression of the link 42 in order to allow some forward and aft movement of the wheel 34 and hub 30 in order to absorb some shock loading experienced by the chassis 20 when encountering large obstacles or bumps such as kerbs at higher speeds. This movement should be small compared to the vertical movement. The resilient portion 44 may comprise a sprung telescopic section of the link 40 or one or more resilient elements 48 held between one or more link platforms 46 and the chassis 20 at a link connection 27 of the chassis 20. The elastomer elements 48 may be elastomer rings 48 surrounding the second link 42 and the link connection 27 may comprise a link aperture 29 through which the second link 42 passes and surrounded by a link platform 31. The link platform 31 having a first side 31a and a second side 31b. Each for supporting one of the one or more elastomer elements 48 against one of the one or more link platforms 46. Preferably, one of the one or more elastomer elements 48 is held between the first side 31a of the link platform 31 and a first platform 46a and a second of the one or more elastomer elements 48 between the second side 31b of the link platform 31 and a second platform 46b of the second link 42. In order to provide fore aft compliance in the first link 41 the pivot connection 26 may include a resilient bush 28 for allowing for aft rotation or compliance about a vertical axis B coincident with axis A. Figure 5 shows a section view vertical and perpendicular to the central plane P taken along line S-S shown in figure 4 through the first link 41 of the linkage 40 and the ride height control means 60. Figure 5 shows two suspension systems 10 according to the current invention one to the left side of the central plane P and one to the right side of the central plane P. The suspension system 10 on the left side is in the second ride height position 12 and the suspension system 10 on the right side of central plane P is in the first compressed position 11. Each suspension system 10 shown includes a ride height control means 60. The ride height control means 60 includes a first portion 70 connected to and movable by the linkage 40 that could also be connected to and movable by the hub 30 and a second portion 80 connected to and movable by the chassis 20. The ride heat control means 60 includes a compression resilient element 64 for supporting the quadricycle 1 above the ground and a compression resilient element 66 for controlling a hub 30 and corresponding wheel 34 dropping when it is not supported by the ground G. In the embodiment shown in figure 5 the first portion 70 is connected to the linkage 40 or the hub 30 and the second portion 80 connected to the chassis 20, it will be understood that in an alternative embodiment these positions could be reversed within the scope of the current invention and the first portion 70 be to the connected chassis 20 and the second potion 80 be connected to the linkage 40 or the hub 30. Figure 5 shows a preferred embodiment wherein the first portion 70 is fixed to an moveable with the linkage 40 and the second portion 80 is fixed to and movable with the chassis 20. Fixed to herein means rigidly connected to rather than pivotally or otherwise connected to. The first portion 70 comprises a first part 70a and a second part 70b having a fixed spatial relationship, or fixed distance therebetween when in use. The first part 70a is proximal the part to which the second portion 70 is mounted and the second part 70b is distal the part to which the first portion is connected or fixed. In Figure 5 the first portion 70 is connected to and fixed to the linkage 40. The bump resilient element 64 is located between the first part 70a of the first portion 70 and the second portion 80 and the extension resilient element 66 is located between the second part 70b of the first portion 70 and the second portion 80. The bump or compression resilient element 64 is compressed between the first part 70a of the first portion 70 and the second portion 80 when the suspension system 10 moves from the second ride height position 12 towards a first compressed position 11. The rebound or extension resilient element 66 is compressed between the second part 70b of the first portion 70 and the second portion 80 when the suspension system 10 moves towards the third extended position 13 from the second ride height position 12. The bump resilient element 64 has a spring rate or stiffness KB and the extension resilient element has a spring rate or stiffness of KR. Preferably KB is greater than KR as in the bump resilient element 64 is stiffer than the extension resilient element 66. The compression resilient element 64 and extension resilient element 66 may be a spring, such as a coil spring, an elastomer such as a Pll elastomer or other suitable resilient material or springing medium. The first portion 70 of the ride height control mechanism 60 includes a first compression platform 72 and a first extension platform 74 connected to and preferably having a fixed relationship to and movable with the first compression platform 72 in use. The second portion 80 of the ride height control mechanism 60 includes a second compression platform 82 and a second extension platform 84 connected to and preferably having a fixed relationship to and movable with the second compression platform 82 in use. The first part 70a of the first portion 70 comprises the first compression platform 72 and the second part 70b of the first portion 70 comprises the first extension platform 74. The first compression platform 72 faces the second compression platform 82 and the bump resilient element 62 is located therebetween. The first extension platform 74 faces the second extension platform 84 and the extension resilient element 64 is located therebetween. The first compression platform 72 and the first extension platform 74 are at least opposing faces, facing toward each other and having a fixed relationship between them in use, with the second compression platform 82 and second extension platform 84 therebetween. The second compression platform 82 and the second extension platform 84 are at least opposing faces having a fixed relationship in use and preferably opposing faces of a unitary component facing away from each other as shown in figure 5. The second compression platform 82, the bump resilient element 62, the first compression platform 72, the first extension platform 74, the extension resilient element 64 and the second extension element 84 are arranged in the given sequence to form a stack 66 having a stack length LS. The bump resilient element 64 has an open length LB and the extension resilient element 66 has an open length LR. Preferably the stack 66 is a linear coaxial stack 66. There is a distance D1 between the first compression platform 72 and the second compression platform 82 and a distance D2 between the first extension platform 74 and the second extension platform 84. In use (D1 + D2) <(LB + LR) such that when there is no input in to the system, meaning no load placed on the bump resilient member 62 and the extension resilient member 64, each has a length of less than LB and LR respectively. This position would be a third extended position 13. When in the second ride height position 12 the weight of the quadricycle 1 places a load through the suspension system 10 and the ride height control means 60 causing the bump resilient element 62 to compress and the extension resilient element 64 to extend. At a first compressed position 12 the bump resilient element 62 will compress and the extension resilient element 64 will have its free length LR and there bay even be a gap between the extension resilient element 64 and one or more of the first extension platform 74 and the second extension platform 84. The first portion 70 of the ride height control means includes a stack length adjustment means 90 for controlling the distance between the fist compression platform 72 and the first extension platform 74 and thus changing both length LS and distances D1 and D2. The effect of the stack length adjustment means is to control the amount that the two resilient elements 62, 64 interact. By reducing LS the bump resilient element 62 is preloaded against the extension resilient element 64. Preferably the stack length adjustment means 90 comprises a rod 92 as shown on the left side of figure 5 or a cylinder 93 as shown on the right side of figure 5 and an adjustor 97 for varying the distance between the first compression platform 72 and the first extension platform 74. Preferably, the rod 92 or cylinder 93 comprises a first end 94 connected to one of the first compression platform 72 or the first extension platform 74 and a second end 96 having a threaded potion 95 for receiving an adjustor 97 having complementary thread and connected to the other of the first compression platform 72 or the first extension platform 74 in order to control the distance therebetween. Preferably the stack length adjustment means 90 is used to adjust LS such that when at the second ride height position 12 the compression resilient element is holding the weight of the quadricycle 1 and the extension resilient element 64 is not under load. Thus in the second ride height position D2>LR and preferably D2=LR. This being the case, when moving from the second ride height position 12 to the first compression position 11 the extension resilient member 64 has no effect and the wheel rate is R1. When the suspension system 10 is moving from the first compressed position 11 to the third extended position 13 at some point D2=LR any further extension beyond this point will result in D2<LR. The compression resilient element 62 will initially still be compressed due to supporting a portion of the mass of the quadracycle 1 and will also be restricted by compressing the extension resilient member 64 as D1<LB and D2<LR this is referred to herein as the third extended position 13 . At this point as the bump resilient element 62 and the rebound resilient element are acting against each other thus the stiffness of the ride height control means 60 will be the rate of each of the resilient elements 62, 64 combined i.e. KB+KR and the wheel rate will be R3. The wheel rate of the system at the second ride height position 12 depends on D2 at position 2. If D2 >=LR then R2 = R1 as only the bump resilient element 62 is active and if D2<LR then R2 = R3 as both resilient elements 62, 64 will be active. Thus changing stack length changes the point in the travel of the suspension system 10 where the wheel rate changes from R1 to R3. From the point D2=LR in the second ride height position 12, reducing the stack height LS further will also have the effect of changing the second ride height position 12 as reducing LS increases the force the extension resilient element 64 exerts on the bump resilient element 62 compressing the bump resilient element 62 further and moving the second portion 80 toward the first part 70a of the first portion 70 and thus reducing the ride height of the quadricycle 1. Accordingly the ride height control means 60 may include one or more ride height adjustment spacers 65. These may be located between the first compression platform 72 and the second compression platform 82 or under the first compression platform 72. Increasing the thickness of a ride height adjustment spacer 65 will increase the ride height. The rod 92 of the stack length adjustment means 90 may pass through an aperture in the middle of the bump resilient element 62 and / or the extension resilient element 64 and serve the additional purpose of locating said resilient elements 62, 64. The cylinder 93 may extend circumferentially about the bump resilient element 62 and / or the extension resilient element 64 and serve the additional purpose of locating said resilient elements 62, 64. In a preferred embodiment the stack 66 and or the stack length adjustment mechanism 90 extends tangentially to the axis of rotation A. Figures 6 to 9 show the ride height control means 60 in different positions. Figure 6 shows the ride height control means 60 disassembled or with the preload on the resilient elements 62, 64 removed such that all the components are touching but none of the resilient elements 64, 66 deformed. LS is thus the free length of the stack 66 with LB + LR = D1 + D2. Figure 7 shows the ride height control means 60 according to the current invention in the third extended position 13. The stack height control means 90 is adjusted to preload the stack by reducing the distance between the first compression platform 72 and the first rebound platform 74 and thus preload the bump resilient element 62 against the extension resilient element 63. LS is less than the free length of the stack 66, (LB + LR) >(D1 + D2), D1 <LB and D2 <LR. In this arrangement the wheels rate is R3. Figure 8 shows the ride height control means 60 in the second ride height position 12. Load from the weight of the quadricycle 1 has caused the bump resilient element 62 to compress between the first part 70a of the first portion 70 and the second portion 80 of the ride height control means 60. The extension resilient element 66 has length LR as it is free or not under load as D2 >= LR. Most preferably at the second ride height position 12 the resilient element 66 has length LR and is in contact with the second part 70b of the first portion 70 and the second portion 80 as D2 = LR. This is achieved through adjusting LS using the stack height control means 90 such that D2 = LR in the second ride height position 12. LS is the same as figure 7 as in use the distance between the first part 70a and the second part 70b of the first portion 70 of the ride height control means is fixed in use thus (D1 + D2) is also the same as figure 7. The bump resilient element 62 is compressed further than in figure 7 thus it remains that D1 <LB Figure 9 shows the ride height control means 60 in a first compressed position 11. The bump resilient element 62 is further compressed still than in figure 8 as it is under greater load from the chassis 20 of the quadricycle or the wheel 34 for example hitting a bump. The extension resilient element 66 has length LR as it is free and not under load as D2 is greater than in figure 7 D2 » LR. LS is again the same as figure 7 as in use the distance between the first part 70a and the second part 70b of the first portion 70 of the ride height control means is fixed in use thus (D1 + D2) is also the same as figure 7. In this arrangement the wheel rate is R1. In the arrangements above R1 <R3 and R2 = R1. Figures 10 and 11 show a side view of a second embodiment of the current invention comprising a quadricycle 1 equipped with a suspension system 10 according to the current invention. The quadracycle 1 shown is a cargo carrying electrically assisted quadricycle 1 However, the current invention could be used with any type of quadricycle 1 or tricycle. The suspension system 10 comprises a chassis 20, a hub 30 suitable for rotatably mounting a wheel 34 thereto and a suspension linkage 40 extending between the hub 30 and the chassis 10. The suspension linkage 40 is rotatably mounted to the chassis 20. The chassis 20 has a front end 22 and a rear end 24 and a central vertical plane P extending longitudinally from said front end 22 to said back end 24. The hub 30 includes fixings 32 for mounting a wheel 34 thereto. Figure 10 shows a side view of a quadricycle 1 in an unladen state. Figure 11 shows a side view of a quadracycle 1 in a laden state. The hub 30 includes a steering pivot 36 about which the wheel 34f may rotate in order to steer the quadricycle 1. The steering pivot 36 has a steering axis of rotation S inclined to the vertical in the direction of plane P in order to provide a caster angle a. In the unladen state caster angle a <0.5 degrees and in the laden state a >1 degrees and preferably a >1.5 degrees. This increase in caster angle provides the benefit of an increase in steering effort for the user in the laden state. In Figure 10 the caster angle a = 0 for providing a low steering effort. Therefore, indicating to the user that the vehicle is laden and will not handle or stop in the same fashion as when unladen. The suspension system 10 includes one or more front linkages 40f for connecting a plurality of front hubs 30f to the chassis 20 and having a front ride height control means 60f providing a front wheel rate RF. The suspension system further includes on or more rear linkages 40r for connecting a plurality of rear hubs 30r to the chassis 20 and having a rear ride height control means 60r for providing a rear wheel rate RR. Wherein RF is greater than RR. It is further preferably that the rear wheel rate RR provided by the rear ride height control means 60r is rising rate when compressed further from the second ride height position 12. Thus as the rear ride height reduces from the second ride height position 12 to a first compressed position 11 the wheel rate RR increases and further preferably increases further still as the rear ride height decreases. Thus it can be said the rear ride height control means 60r has a rising rate in compression. The chassis 20 may include a cargo carrying space 100 having a centre of plan area V, a front axle line FA passing through the front hubs 30f and a rear axle line RA passing through the rear hubs 30r and a wheel base length W between FA and RA; wherein V is located rearward of 90% of W from FA and preferably vertically above RA. Thus at least 90% of the weight of the load carried in the cargo carrying space 100 is directed through the rear axle to the rear hubs 30r and the rear ride height control means 60r. This causes the rear end 24 of the chassis 20 to drop a greater distance than the front end 22 of the chassis 20 when laden resulting in an increase in the front caster angle a Any system feature as described herein may also be provided as a method feature, and vice versa. As used herein, means plus function features may be expressed alternatively in terms of their corresponding structure. Any feature in one aspect may be applied to other aspects, in any appropriate combination. In particular, method aspects may be applied to system aspects, and vice versa. Furthermore, any, some and / or all features in one aspect can be applied to any, some and / or all features in any other aspect, in any appropriate combination. It should also be appreciated that particular combinations of the various features described and defined in any aspects can be implemented and / or supplied and / or used independently.

Claims

1. A suspension system (10) for a quadricycle (1) having a first compressed position (11), a second ride height position (12), a third extended position (13) and a wheel rate (R); comprising:a chassis (20) having a front end (22) and a rear end (24) and a central vertical plane P extending longitudinally from the front end (22) to the back end (24), a hub (30) having fixings (32) for rotatably mounting a wheel (34) thereto, a suspension linkage (40) extending between and the hub (30) and the chassis (20) and rotatably mounted to the chassis (20), a ride height control means (60) comprising a first portion (70) connected to and moveable by the chassis (20) or one of the hub (30) and suspension linkage (40) and a second portion (80) connected to and movable by the other of the chassis (20) or one of the hub (30) and suspension linkage (40), a bump resilient (64) element located between a first part (70a) of the first portion (70) and the second portion (80) and an extension resilient element (66) located between a second part (70b) of the first portion (70) and the second portion (80);wherein the bump resilient element (64) is compressed when moving from the second ride height position (12) toward the first compressed position (11); andthe extension resilient element (66) is compressed when moving from the second ride height position (12) toward the third extended position (13).

2. A suspension system (10) according to claim 1 having a first wheel rate R1 in the first compressed position (11), a second wheel rate R2 in the second ride height position (12) and a third wheel rate R3 in the third extended position (13);wherein R3 is greater than R1.

3. A suspension system (10) according to claim 1 or claim 2 wherein the first wheel rate R1 is equal to the second wheel rate R2.

4. The suspension system (10) according to any previous claim wherein the bump resilient element (62) has a spring rate KB and the extension resilient element (64) has a spring rate KR and KB >KR for a given deflection.

5. The suspension system (10) according to any previous claim wherein the bump resilient element (62) has an open length LB and the extension resilient element (64)has an open length LR and at the second ride height position (12) the extension resilient element has length LR.

6. A suspension system (10) according to any previous claim wherein the first portion (70) of the ride height control means (60) includes a first compression platform (72) and a first extension platform (74) connected to and movable with the first compression platform (72);The second portion (80) of the ride height control means (60) includes a second compression platform (82) and a second extension platform (84) connected to and movable with the second compression platform (82); and whereinthe first compression platform (72) faces the second compression platform (82) and the bump resilient element (62) is located therebetween; andthe first extension platform (74) faces the second extension platform (84) and the extension resilient element (64) is located therebetween.

7. The suspension system (10) according to any one of claim 4 to 6 wherein the first compression platform (72), the bump resilient element (62), the second compression platform (82), the second extension platform (84), the extension resilient element (64) and the first extension platform (74) are arranged in the given sequence in a linear coaxial stack (66) having a length LS.

8. The suspension system (10) according to claim 7 wherein the second compression platform (82) and the second extension platform (84) comprise opposite sides of a unitary component.

9. The suspension system (10) according to any previous claim wherein the first portion (70) of the ride height control means (60) is fixed to and moveable with the chassis (20) or one of the hub (30) and suspension linkage (40) and the second portion (80) is fixed to and movable with the other of one of the hub (30) and suspension linkage (40) or the chassis (20),9. The suspension system (10) of any one of claims 6 to 8 wherein there is a distance D1 between the first compression platform (72) and the second compression platform (82) and a distance D2 between the second extension platform (76) and the first extension platform (74) and D1+D2<LB+LR.10 The suspension system (10) of claim 9 wherein at the second ride height position (12) approximately distance D2=LR.

11. The suspension system (10) of any one of claims 7 to 10 wherein the first portion (70) of the ride height control means (60) includes a stack length adjustment means (90) for controlling the distance between the first compression platform (72) and the first extension platform (74) and thus (D1+D2).

12. The suspension system (10) of claim 11 wherein the stack length adjustment means (90) comprises a rod (92) or a cylinder (93) having a first end (94) connected to one of the first compression platform (72) or the first extension platform (74) and a second end (96) having a threaded portion (95) for receiving an adjuster (97) having a complementary thread and connected to the other of the first compression platform (72) or the first extension platform (74) in order to control the distance there between.

13. The suspension system (10) of any previous claim wherein the linkage (40) is connected to the chassis (20) at a pivot mount (26) having an axis of rotation A extending longitudinally relative to the chassis (20) about which the linkage (40) may rotate.

14. The suspension system (10) of any one of claims 10 to 13 wherein the stack (66) and / or stack length adjustment means (90) extends tangentially to the axis of rotation A.

15. The suspension system (10) of any one of claims 6 to 14 wherein the ride height controlmeans (60) includes one or more ride height adjustment spacers (65) between the first compression platform (72) and the second compression platform (82).

16. The suspension system (10) of any one of claims 12 to 15 wherein the bump resilient member (62) and the extension resilient member (63) extend about the rod (92) or circumferentially within cylinder (93) such as to be located thereby.

17. The suspension system (10) of any preceding claim wherein the bump resilient member (62) and the extension resilient member (63) comprise a coil spring, an elastomer or other suitable resilient member.

18. The suspension system (10) of any preceding claim wherein the link (40) is a swing arm, fixed to the hub (30).

19. The suspension system (10) of any one of claims 13 to 18 wherein the pivot mount (26) includes a resilient bush (28) allowing compliance in the linkage (40) about a vertically extending axis B.

20. The suspension system (10) of any preceding claim and the linkage (40) comprising a first link (41) extending from the chassis (20) in a lateral direction having a first end (41 ib) connected to the chassis at a point M and a second end (41 ob) connected to the hub (30);A second link (42) extending in a lateral direction from the chassis (20) and having a first end (42ib) connected to the chassis (20) at a point T and a second end (42ob) connected to the hub (30) and or to the first link (41) proximal the second end (41ob) of the first link (41);wherein T is offset toward the front end (22) or the rear end (24) of the chassis (20) relative to M and the second link (42) includes a resilient portion (44) for allowing extension and compression of the second link (42).

21. The suspension system (10) of claim 20 wherein the resilient portion (44) of the second link (42) comprises one or more elastomers between one or more platforms (46) and the chassis (20).

22. The suspension system (10) of any preceding claim wherein the link (40) extends laterally from the chassis (20) perpendicular to the central plane P.

23. The suspension system (10) of any preceding claim wherein the first portion (70) of the ride height control means (60) is fixed to and moveable with the linkage (40) and the second portion (80) of the ride height control means (60) is fixed to and moveable with the chassis (20).

24. The suspension system (10) of any preceding claim wherein the hub (30) includes a steering pivot (36) about which the hub (30) may rotate having a steering axis of rotation S inclined to the vertical in the direction of plane P a caster angle a;wherein in the unladen state a <0.5 degree and in the laden state a >1.

25. The suspension system (10) of any preceding claim wherein the linkage (40) includes one or more front linkages (40f) for connecting a plurality of front hubs (30f) to the chassis (20) having a front ride height control means (60f) providing a front wheel rate RF and one or more rear linkages (40r) for connecting a plurality of rear hubs (30r) to the chassis (20) having a rear ride height control means (60r) providing a rear wheel rate RR;wherein RF is greater than RR.

26. The suspension system (10) of claim 24 or claim 25 wherein the chassis (20) includes a cargo carrying space (100) having a centre of plan area V, a front axle line FA passing through the front hubs 30f, a rear axle line RA passing through the rear hubs 30r and a wheel base length W between FA and RA; wherein V is located rearward of 90% of W from FA and preferably vertically above RA for passing the load from said cargo through the rear hubs 30r.

27. A suspension system (10) for a quadricycle (1) having a first compressed position (11), a second ride height position (12), a third extended position (13) and a wheel rate (R); comprising:a chassis (20) having a front end (22) and a rear end (24) and a central vertical plane P extending longitudinally from the front end (22) to the back end (24),a plurality of front hubs (30f) having fixings (32) for rotatably mounting a wheel (34) thereto, a steering pivot (36) about which the hub (30) may rotate having a steering axis of rotation S inclined to the vertical in the direction of plane P a caster angle a;a plurality of rear hubs (30r) having fixings (32) for rotatably mounting a wheel (34) thereto;a suspension linkage (40) extending between each of the hubs (30f, 30r) and the chassis (10) and rotatably mounted to the chassis (20);wherein in the unladen state a <0.5 degree and in the laden state a >0.5 degree and preferably a >1.

28. The suspension system (10) of claim 27 wherein the linkage (40) includes one or more front linkages (40f) for connecting a plurality of front hubs (30f) to the chassis (20) having a front ride height control means (60f) providing a front wheel rate RF and one or more rear linkages (40r) for connecting a plurality of rear hubs (30r) to the chassis (20) having a rear ride height control means (60r) providing a rear wheel rate RR; wherein RF is greater than RR.

29. The suspension system (10) of claim 27 or claim 28 wherein the chassis (20) includes a cargo carrying space (100) having a centre of plan area V, a front axle line FA passing through the front hubs 30f, a rear axle line RA passing through the rear hubs 30r and a wheel base length W between FA and RA; wherein V is located rearward of5 90% of W from FA and preferably vertically above RA for passing the load from saidcargo through the rear hubs 30r..

30. The suspension system (10) of any one of claims 24 to 30 wherein >90% and preferably >98% of the load from the cargo carrying space (100) is directed through io the rear hubs (30r)31. The suspension system (10) of any one of claims 24 to 31 wherein the rear ride height control means (60r) has a rising spring rate preferably from the second ride height position 12.1532. A quadricycle (1) having a suspension system (10) of any one of claims 1 to 31.

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