Abstract:
A suspension system for isolating a load (L) independently from two separate inputs (I A , I B ), such as a pair of wheels. A slider ( 19 ) is slidably mounted to a frame member ( 11 ) supporting the load and pivotable supports a common swing-arm ( 23 ). Each end of the common swing-arm is coupled to corresponding input swing-arms by a linkage assembly ( 24 ) comprising a pair of link-arms ( 25 A,  25 B) in a manner that an input disturbance will be transferred by the corresponding input swing-arm to its link-arm which will cause a positive translation and rotation movement of the the common swing-arm relative to the the frame member, such that the common swing-arm will pivot a certain degree about the other link-arm but without substantially moving the latter, thereby maintaining the undisturbed input independent from the disturbed input. The suspension system may be applied to bicycles, motor-cycles, automobile axles and rolling vehicles in general.

Description:
FIELD OF THE INVENTION 
     The present invention generally refers to a suspension system wherein two inputs are applied to a common load suspension device. In particular, the system of the invention may be applied to land vehicles; more particularly to bicycles, motor-cycles and automobiles. 
     In the case of two-wheeled vehicles, such as bicycles and motor-cycles in particular, the suspension system may serve to isolate the seat and handlebars from each of the front or back wheels. In a four-wheel vehicle, the system may be applied to either or both the front and/or rear axles or to the left- and right-hand side pairs of wheels. 
     The shock-absorber function, within the context of the present invention, is related to dampening movement transmitted from a movable part to another part supported thereon or otherwise connected thereto. Likewise, the function of the spring is to maintain support of the movable part at a predetermined height or distance from the other part, by resiliently restoring the movable part back to its original placement once the external force causing movement thereof has ceased. 
     BACKGOUND OF THE INVENTION 
     Vehicles generally have separate suspension devices comprising springs or springs and shock absorbers in combination, for each wheel or axle end. Such devices are technically well developped and relatively costly. In lightweight vehicles requiring suspension, such as in mountain bicycles for instance, the weight of the suspension device is also a relevant factor. 
     Some automobile vehicles use common interliked resilient devices, however for design purposes each half-spring is considered as a separate resilient element pertinent to a separate wheel or wheel system. Such separate devices are even more apparent in two-wheel vehicles. Most motor-cycles and some bicycles supplied with full suspension means use a wheel suspension system provided with a telescopically coupled sliding tube and a fork leg forming a suspension assembly with a shock absorber assembly. The size of the conventional tube/fork system requires overdimensioning to resist strong shocks which tend to bend the arrangement. Another consideration is that the optimum angle of direction does not coincide with the optimum angle of operation. 
     U.S. Pat. Nos. 4,265,329 and 4,627,632 suggest articulated systems that purport to overcome these problems. Further solutions are disclosed in U.S. Pat. Nos. 4,542,910 and 4,712,638 wherein a progressive linkage mechanism is incorporated between the frame structure of the vehicle and the swing arm which provides a point of progressive movement relative to the movement of the swing arm. A cushion member is coupled at such a point rather than directly to the swing arm to obtain an advantageous response relationship to movement of the swing arm. In this way, the vehicle provides a more comfortable or pleasing ride on a wider range of road conditions while maintaining a low weight. There is also in the art a wide range of simple and complex suspension systems for the back wheel. 
     Pedalling is the cause of a further problem in the case of bicycles. Many rear suspension are made with the pivot point at the same height as the rear wheel axle and/or about the crank assembly center. As soon as the rear axle goes above the pivot point, the chain force tends to pull the suspension into further compression. This exaggerates the suspension and creates a sagging effect that can be felt when pedalling. Furthermore, there is a loss of pedalling energy. To overcome these problems, the pivot point of many suspension units have been raised above the front chain ring. By doing this, the sag effect and the pull on the suspension is reduced or eliminated, such as suggested in U.S. Pat. No. 5,725,227 or in U.S. Pat. No. 5,685,553. 
     Another problem associated with this type of suspension is that the swing arm is parallel to the ground. When the rear wheel hits a bump, the resultant force is generally at a 15° to 20° angle to the ground. Thus, a substantial portion of the resultant force pulls on the swing arm and slows the rider down. In these systems, the resultant force on the rear wheel from hitting a bump is more perpendicular to the swing arm. This reduces the backward pull on the swing arm and the bicycle. However, during the compression travel of the rear wheel, these suspension systems tend to force the rear wheel in a backward direction which applies tension on the chain. Thus, the chain tension hinders the movement of the suspension, particularly at the upper end of the compression travel. U.S. Pat. Nos. 5,791,674 and 5,452,910 disclose articulated systems wherein the rear swing arm trasero does not follow a circular path through a pivot, thereby reducing forces transmitted to the frame by pot-holes and reducing the ziz-zag effect caused by pedalling. This eefect is also addressed by U.S. Pat. No. 5,785,339 which discloses a more complex system. 
     This brings us to the desire to simplify suspension systems by using a common resilient restoration and shock absorber for both wheels, as suggested in U.S. Pat. Nos. 5,498,014, 5,330,219, 5,772,227 and 5,417,445, as well as in U.S. Pat. Nos. 4,583,612 and 4,378,741 using different suspension device elements. However, in all these cases, the uses of a single suspension device common to both separate inputs causes cross-effects from each input to the other, therefore the inputs in such patented systems may not be considered independent of each other. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a suspension system wherein two separate input nodes may be independently coupled to a vehicle frame using a single suspension device. 
     Another object of the present invention is a system for use in a two-wheel vehicle or cycle for providing front and rear wheel suspension to the cycle frame by means of a single spring means, with or without complementary shock absorbing means. 
     A further object of the present invention is a system for use in a multiple two-wheel axle vehicle for providing independent suspension for each wheel of an axle thereof to a vehicle chassis or body through a common spring and shock absorber means. 
     Yet a further object of the invention is to provide a simpler and more economical suspension system. 
     The suspension system of the invention generally comprises a frame member to which a pair of separate input nodes are pivotable connected such as by means of a pair of input swing-arms. The frame member forms part of a generally static load system which includes the means accomodating the vehicle passengers in transit. According to the present invention, the suspension system further comprises a common swing-arm pivoting on a slider mounted to said frame member, such that the swing-arm may pivot and translate in a predetermined direction in relation to the frame member. The slider is coupled to the frame member by means of a suspension device which may include a resilient member or a resilient/shock absorber combination. The swing-arm includes two further pivots on each side of the slider pivot for coupling respective link arms to each of said nodes in a configuration such that an external force disturbing one of said nodes causes the common swing-arm to tilt substantially about the link-arm pivot corresponding to the other, undisturbed node, thereby urging the slider against the suspension device. The mechanism essentially formed by the link arms, the common swing arm and the slider provides substantially independent suspension between the frame member and each of the input nodes. 
     The present invention further identifies two inherently stable link arm configurations in particular. In a first embodiment, the slider is located on the frame arm above the pivot connections between the frame arm and the pair of input swing-arms. In this embodiment, the link-arms may cross-over to connect each node to the opposite end of the common swing-arm. In a second embodiment, the slider is located on the frame arm below the pivot connections between the frame arm and the pair of input swing-arms. In this second embodiment, the link-arms connect each node to the end of the common swing-arm on the same side of the frame member as the node. Thus, a condition for unaided stability is that the link-arm configuration be such that a positive (upward) disturbance at one node tends to reduce the angle between the driven link-arm and the common swing-arm, i.e. urges the common swing-arm to align with the driven link-arm. 
     The present invetion is, inter alia, applicable to two-wheel vehicles or cycles wherein the frame member supports the seat. The front and back wheel axles may be considered as the input nodes. In a preferred embodiment, the fork mounting the back wheel axle is adapted as a rear input swing-arm directly pivoted to the frame member. The front fork is generally rigidly connected to the second input swing-arm, the rear end of which is pivotably connected to the rear swing-arm/fork. In this preferred embodiment, the handlebar of the vehicle is not rigidly attached to the front wheel fork as in conventional bicycles and motor-cycles but is connected to the seat. 
    
    
     BRIEF DISCRIPTION OF THE DRAWINGS 
     These and other features, advantages and details of this invention and how it may be reduced to practice may be better understood from the ensuing detailed description, by way of example and by no means limiting, of exemplary embodiments represented in the appended drawings, wherein: 
     FIG. 1 is a schematical representation of the suspension system according to a first embodiment of the present invention, illustrated in an unloaded state. 
     FIGS. 2A and 2B are schematical representations of the suspension system of FIG. 1 responding to a balanced input state, i.e wherein both the input nodes are subjected to respective external input forces of like magnitude and direction. 
     FIG. 3 is a schematical representation of the suspension system according to a second embodiment of the present invention, illustrated in an unloaded state. 
     FIG. 4 is a schematic representaton of a suspension system similar to FIG. 1 adapted to the frame of a two-wheel vehicle, such as a bicycle or a motor-cycle. 
     FIGS. 5A and 5B are a schematic representaton and a perspective view of a suspension system similar to FIG. 3 adapted to the rear suspension of a automobile or a truck. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A first embodiment of the suspension system is shown in FIG. 1 in a relative unloaded state. A load L requiring independent suspension from two separate inputs I A  and I B  is supported by a reference frame member  11 . The load L may comprise a plurality of discrete components and may be rigidly attached to the frame member. Moreover, merely for convenienced purposes, the load L appears in a centred on the frame member  11  however, as will usually be the case in practice, the load L may alternatively be eccentric relative to the frame member. 
     A pair of pivots  13 A and  13 B at the bottom end of the frame member  11  connect the latter to a pair of input swing-arms  15 A and  15 B the free ends of which incorporate the input nodes I A  and I B . Although the input nodes I are depicted in the drawings at a certain point on their assosciated swing-arm  15  (alphabetical suffices A, B are often omitted herein when generalizing), the input I may be applied at any point or distributed over multiple points of the input swing-arm  15  spaced from the frame pivot  13 . 
     Moreover, two separate pivot connections the pivot  13 A and  13 B are shown in the drawings, however they may be combined into a single triple-pivot connections. Alternatively, as further apparent from the disclosure hereinafter, the connection of a input swing-arm  15  to the frame member  11  need not necessarily be direct. 
     The term “bottom” is used herein in a relative sense consistent with the preferred vehicle applications of the invention described hereinafter. Thus, a “positive” disturbance force applied to any one of said nodes I A  or I B  is assumed to have a component in the “upward” direction. Nonetheless, although the suspension system of the invention is disclosed lying generally in an ideal vertical plane, the system may lie eventually in a horizontal plane according to a particular application requirement, hence the use of the “positive” rather than upward. Naturally, in these vehicle embodiments, computer simulation has shown that the inputs may be briefly negative (such as going down a step), however the magnitudes thereof are smaller compared to the positive inputs and have no substantial impact on design considerations. 
     The frame member  11  is attached to one side of a suspension device  17  including a resilient component or spring S. Preferably, a shock absorber M is added in combination, e.g. in parallel, to the spring S. Both componentes S and M may be of conventional design. 
     The other, movable side of the suspension device  17  is attached to a slider  19  slidably mounted to the frame member  11 . The slider  19  features a pivot  21  to which a swing-arm  23  is mounted, such that the swing-arm  23  may slide up and down the frame member  11  and rotate about this locus. The slider the slider  19  is driven in this manner by a linkage system  24  according to the invention comprising a pair of link-arms the link-arm  25  arranged as depicted in FIG.  1 . In particular, there is one link-arm  25 A with pivot connections  27 A,  29 B at each end coupling one of the swing-arms  15 , or nodes I for that matter, to the opposite end of the swing-arm  23 . Likewise, the other link-arm  25 B has a pivot connection  27 B to the swing-arm  15 B and another pivot connection to the common swing-arm  23 . 
     Although the frame member  11  is depicted as a bar-shaped member, it is in no way restricted to this shape and may have a different shape as required by a specific application. For instance, the slider function may be embodied by an elongated hole formed in a plate-shape frame member to hold central pivot means  21 . 
     The suspension system adopts the position shown in FIG. 1 in an unloaded state, i.e. when I A =I B =0 (relative) is steady. FIG. 2A illustrates the system response to a balanced input applied at both nodes I A  and I B  simultaneously. The upward movement of the input swing-arms caused by the positive application of external disturbances F A =F B ≠0 is transferred by the link-arms  25  to the swing-arm  15 . Each link arm the link-arm  25  applies on the corresponding end of the common swing-arm  23  a vertical force component directed upwards and a vertical force component directed inwards, i.e. towards the central pivot  21 . The symmetrical vertical components from each link-arm the link-arm  25  cancel each other out therby resulting in double upward resultant force on the slider  19  and a torque on the common swing-arm  23 . The torques are of opposite signs thereby cancelling out, such that the common swing-arm  23  does not rotate but is driven by the sum of the positive forces, thereby pushing the slider  19  upwards along the frame member locus to compress the suspension device the suspension device  17  a distance X. The normal position (FIG. 1) is restored when the spring S is compressed sufficiently to return a force F S =kX equal said sum, i.e. when the spring compression X=2F A /k. The overall effect (i.e. vibration amplitude, frequency and decay) on the load L, and the amount of spring compression X, depend mainly on the magnitude and duration of the input disturbance and the load (including the frame) weight and inertia. 
     Of particular interest is the response to an unbalanced dual input, since this represents a frequent if not constant situation in practice and concerns a primary object of the invention. As illustrated in FIG. 2B, one of the nodes I B  is subjected to a positive disturbance F B ≠F A . The swing-arm  15 B pivots upwards and, through rigid link-arm the link-arm  25 B, pushes the opposite side common swing-arm  23 , causing the latter to rotate since there is no countertorque on the other end thereof. The common swing-arm  23  rotates in a direction which tends to align it with the driving link-arm  25 B. As the angle between the common swing-arm  23  and the link-arm  25 B diminishes due to the rotation, the tangential component generating the torque on the former diminishes until the torque is matched by a countertorque which the restoring force transmitted from the suspension device  17  applies to the common swing-arm  23  via the central pivot  21 , whereby the arm  23  stops tilting. The system therafter reacts to restore to the normal position. 
     Actually, the common swing-arm  23  substantially rotates on the pivot  29 A at its opposite end, thereby dragging the slider  19  upwards and urging the required reaction from the suspension device the suspension device  17  to cushion the effect of the input F B  on the load and and restore the normal position thereof. In fact, there is hardly any noticeable movement on the undisturbed link-arm  25 A and swing-arm  15 A side, except generally negligible movement coming from the frame member  11  shifting upwards slightly. 
     This is one of the primary advantages of the system of the invention and may be interpreted in that the undisturbed pivot connection  29 A is practically in the same relative position in FIGS. 1 and 2A. Thus the undisturbed input node I A  is substantially independent from disturbaions applied at the opposite input node IB, and vice versa of course. In the case of composite disturbances 0&lt;F B ≠F A &gt;0, the linkage system  24  responds independently to each input I and the dynamics of the suspension device  17  are simply a composition of the responses of FIGS. 2A and 2B. 
     For some applications it may be desirable to locate the suspension device  17  and the common swing-arm  23  underneath the input swing-arms  15 . FIG. 3 illustrates an alternative embodiment useful for such applications. The slider  19  is located on the bottom part of the frame member  11  and a different linkage arrangement  24 ′ is required to ensure an inherent stable suspension system. The stability condition may be expressed as that the link-arms  25  should be arranged such that, in response to an external disturbance at one of the nodes I, the common swing-arm  23  tends to align itself, or close the angle, with the disturbed link-arm  25 . To satisfy this condition, each link-arm should be connected to the end of the common swing-arm  23  on the same side of the associated input swing-arm  15  relative to the frame member  11 . 
     If a linkage arrangement not meeting this condition is used, the system would tend to destabilize under disturbance, thereby requiring additional components to avoid the common swing-arm  23  from flipping over. 
     Reference is made hereinafter to particular applications of the suspension systems described hereinabove. Like reference numerals are used in FIGS.  4  and  5 A- 5 B to identify equivalent components relative to the systems of FIGS. 1 or  3 . 
     FIG. 4 refers to a particular application of the suspension system of the invention to a bicycle or motor-cycle. For ease of illustration and clarity, only the relevant parts of the cycle are represented. The cycle comprises a frame member the frame member  11  including means  31  for supporting a seat on top and, in the case of a bicycle, means  33  below for holding the pedals. A slider  19  is mounted to the frame member  11  and a spring S between the slider  19  and an upper stop  35  on the frame member  11 . 
     A front fork  37  is conventionally adapted to hold a wheel and is retained inside a tubular housing  39  allowing the wheel to turn sideways by means of handlebars  41  (represented schematically in FIG.  4 ), further reference to which is made hereinafter. The fork housing  39  is rigidly attached to a front swing-arm member  15 F such that disturbances returned by the front wheel (the axle of which may be considered as one of the input nodes I F ) are transferred directly to the arm  15 F. The rear swing-arm  15 R is formed by the back-wheel fork (again, the back-wheel axle may be considered as the other input node I R ). 
     The front fork  15 F is connected via pivot  13 R near the bottom end of the frame member  11 . The pivot connection between the rear swing-arm  15 R is carried out indirectly, by pivoting the front end thereof on the back end of the front swing-arm  15 R at a point  13 R′ spaced backwards from the front swing-arm/frame member pivot  13 F. It has been found that this coupling  13 R′ of the rear fork  15 R on the front swing-arm  15 F assists cycle stability when travelling up and down inclined terrain. 
     As in FIG. 1, a central swing-arm the common swing-arm  23  is mounted on the slider  19  and coupled to the front and rear swing-arms  15  by means of a pair of link-arms  25 F and  25 R via pivots  27 F- 29 F and  27 R- 29 R, respectively. In the cycle embodiment, the central swing-arm the common swing-arm  23  and the link-arms  25  are actually formed by a pair of bars affixed side-by-side to each other and arranged symmetrically on both sides of the plane of the frame member  11 . Although shapes may vary, the shaped of the arms the input swing-arms  15  and the link-arms  25  shown in FIG. 4 are particularly designed to avoid movement of the system in operation from interfering with the normal cycle movements. In one embodiment, each arm  15  and  25  comprises a pair of tubular members made of aluminium alloy and soldered to cross joining members (not illustrated). However, other materials may be used, such as carbon fiber in epoxy resin, titanium alloy, etc. 
     Although the suspension system is shown in FIG. 1 comprising symmetrical components of the same length, the embodiment of FIG. 3 also shows that there is no constraint in this respect. That is, the input swing-arms  15  and the link-arms  25  may be of equal or substantially different lengths, according to specific design considerations. 
     Tests carried out on a bicycle embodied as in FIG. 4 showed that the suspension responded as expected from a computer simulation carried out on the suspension model of FIG.  1 . The front and back wheels were felt to independently copy (i.e. adhere to) the terrain going up and down steps. Visual analysis of video images filmed during these tests confirmed these feelings of the driver on the seat. 
     A further improvement within the present invention concerns the handlebars. Most bicycles and many motor-cycles afford no or scanty suspension to the handlebars in relation to the seat of the vehicle. Therefore, while the passenger or driver may find himself or herself comfortably seated, front wheel shocks, particularly if strong and/or repetitive may be hard on the upper members of the driver. The present invention may also provide suspension for the handlebar with the same suspension device S used for the seat. As show in FIG. 4, rather than conventionally affix the handlebars  41  to the front fork  37 , the handlebar  41  is supported in a housing  43  forming part of or rigidly attached to the frame member  11 . Thus, the frame member  11 , the seat and the handlebars  41  form a load system L for the suspension system of FIG.  1 . Means, such as a hinged member (not illustrated) allowing relative axial movement between the handlebars  41  and the front fork  37 , may connect the handlebar axle to the front fork, to enable the front wheel to turn sideways together with the handlebar. 
     Another improvement within the invention is the provision of means to adapt the same cycle suspension for both uphill and downhill. Heretofore, different competiton bicycles and motor-cycles are used for uphill and downhill, since a substantially stiffer suspension is effective in one case but countereffective in the other. The suspension of the invention embodied in the cycle of FIG. 4 may be stiffened but tightening the central pivot  21 , for instance, thereby holding the central swing-arm  23  fast against the frame member  11 . To adapt to greater suspension requirements, the central pivot may be loosened to enable the common swing-arm  23  to travel up and down the common swing-arm  23  and tilt in relation thereto. 
     FIGS. 5A-5B illustrate an embodiment of the invention applied to a four-wheel vehicle, such as a buggy. To avoid repetitons and obvious deductions on the preceding disclosure herein, only the relevant portions of this embodiment are described hereafter. The essential structure of the suspension system employed is that of the embodiment of FIG.  3 . 
     The vehicle comprises a chassis  11  formed by a tubular structure for supporting the load. The end bars  47  receive the inputs from the wheels and are articulated at joints  49  on the ends of upper and lower bars  15  and  51  which form a parallelogramme structure. Means  53  may be provided for turning the wheel direction. The chassis is provided with the central frame member  11  formng part thereof and mounting the slider  19  and the common swing-arm  23  by means of the latter. Bars  25  embodying the link-arms are provided between the top bar structure  15  and the swing-arm  23 . 
     In the case of a automobile, a similar structure may be adapted further including shock absorber means. 
     Although the present invention has been disclosed in detail in connection with preferred embodiments and specific applications of a suspension system, different modifications in construction, materials, mounting, operation and applications may appear to those skilled in the art without departing from the purview of the claims appended hereto.