LEAF SPRING TRAILER SUSPENSION

Abstract: A trailer includes a frame and a pair of leaf springs extending longitudinally of the frame on respective opposed sides thereof, wherein each leaf spring is cantilevered with one end connected to the frame and with its otherwise free, other end secured to an axle of the trailer.

Description: LEAF SPRING TRAILER SUSPENSION DESCRIPTION This invention relates to a suspension for use with a trailer and is especially, but not exclusively, related to such a suspension for use with a lightweight trailer. At present, there are many forms of suspensions used on trailers of lighter weight, ranging from conventional semi-elliptical, multi-leaf steel springs, which isolate the trailer body from rough road surfaces and which locate the axle with respect to the trailer body or frame, to springing systems using, for example, coil springs and rubber and polymer units which require extra linkages to locate the axle. One of the most common and inexpensive trailer suspensions in current use is the simple conventional multi-leaf spring mentioned above, in which the axle is located transversely of the trailer ancl is mounted at respective opposed ends to the springs generally centrally thereof. Each spring is then mounted to the frame of the trailer using a bracket and bush at one end, usually at the front end of the spring, and a bracket, shackle and two bushes at the other end, usually at the rear end of the spring. With this known type of trailer suspension, a compromise in the load to deflection stiffness ratio, known as the spring rate, is involved. That compromise resides between a spring rate which is as soft as possible to provide the best isolation of the trailer body from rough road surfaces and a spring rate that is as stiff as possible for stability when the trailer is fully loaded, particularly with a high centre of gravity load. For economic reasons, this compromise spring rate has effectively to be constant over the complete load range, namely, from when the trailer is empty to bump inputs when the trailer is fully laden. As a consequence, the isolation, or ride, of the trailer when unladen tends to be very stiff and, therefore, undesirable. Also, to prevent the trailer axle and/or wheels contacting the trailer body or frame during bump inputs, the clearance therebetween has to be larger than is often desirable for access to the trailer, for maintenance purposes and the like. Alternatively or additionally, features which increase the cost and weight of the trailer can be employed, such features including bump stops and/or variable rate springs, to overcome these disadvantages. Accordingly, it is an object of the present invention to provide a trailer suspension, in its various aspects, which overcomes, or at least substantially reduces, the disadvantages associated with the known types of trailer suspension discussed above. It is another object of the invention to provide a trailer suspension, in its various aspects, which is both novel and inventive and which improves the ride and handling of trailers at lower cost, weight and complexity than those of the prior art trailer suspensions discussed above. Thus, a first aspect of the invention resides in a trailer comprising a frame and a pair of leaf springs extending longitudinally of the frame on respective opposed sides thereof, wherein each leaf spring is cantilevered with one end connected to the frame and with its otherwise free, other end secured to an axle of the trailer. A second aspect of the invention provides a suspension for use with a trailer, comprising a pair of leaf springs arranged to extend longitudinally of a frame of, say, a trailer, on respective opposed sides thereof, wherein one end of each leaf spring is arranged to be connected to the frame, such that each leaf spring is cantilevered with respect to the frame, and the otherwise free, other end of each leaf spring is arranged to be secured to an axle. A third aspect of the invention provides, in combination, a pair of leaf springs and an axle, the pair of leaf springs being arranged to extend longitudinally of a frame of, say, a trailer, on respective opposed sides thereof, wherein one end of each leaf spring is arranged to be connected to the frame, such that each leaf spring is cantilevered with respect to the frame, and the otherwise, free other end of each leaf spring is secured to the axle. Thus, the axle is or can be mounted to the trailer in cantilever fashion solely by the cantilevered pair of leaf springs. The axle may be a single axle extending or arranged to extend transversely of the frame of the or a trailer, in which case, the otherwise free, other ends of the leaf springs are connected or connectable to respective opposed ends of the or a trailer axle. Alternatively, a pair of stub axles may be used on respective opposed sides of the or a trailer frame, in which case, the otherwise free, other end of each leaf spring is secured or securable to a respective one of that pair of stub axles. Preferably, the otherwise free, other end of each leaf spring is secured or securable to the or a trailer axle by being wrapped therearound. The one end of each leaf spring which is connected or connectable to the frame of the or a trailer, may be bolted rigidly thereto, preferably directly thereto. Alternatively, the one end of each leaf spring may be connected pivotally to the frame of the or a trailer. In any event, that one end of each leaf spring should be connected or connectable to the or a trailer frame sufficiently securely to withstand the cantilevered transverse, side cornering forces to which the axle is subjected in use. Such connection may be rigid or may be pivotable, as discussed above and to be described in more detail hereinbelow. When the otherwise free, other end of each leaf spring is secured or securable to the trailer axle by being wrapped therearound, any suitable form of securement may be employed. For example, the wrapped-around other end of each leaf spring may be push-fitted, friction-fitted, adhered, puddle or full welded to the axle, bolted to the axle, clip-secured to the axle or any combination thereof. If a through bolt is used, then it would be preferable to have the bolt and associated hole through which the bolt passes extending through the neutral axis, in bending, of the axle, to minimise any high stress concentrations created under laden conditions. The one end of each leaf spring may be connected or connectable to the frame of the trailer in such a manner, that in use and when each leaf spring deflects sufficiently, it can contact the trailer frame, either directly or indirectly, as the load of the trailer increases from unladen to fully laden, thereby reducing the effective working length of each leaf spring and, as a consequence, increasing the stiffness, or rate, thereof. Also, as each leaf spring contacts the trailer frame and, as a result, the effective working length of the leaf spring reduces, the bending stress in each leaf spring is reduced, thus allowing the use of much lighter leaf springs or, indeed, single leaf springs. Thus, the invention can provide a trailer suspension which produces an economic, variable leaf spring rate providing good isolation from a road surface from the unladen to the fully laden conditions, and beyond, of the trailer to reduce any bump or overload deflection of the leaf springs. Each leaf spring may comprise a single leaf spring or a main leaf spring with an additional, auxiliary leaf spring for pre-loading the main leaf spring, to prevent, or at least substantially reduce, deflections of the main leaf spring which are too high between unladen and fully laden conditions of the trailer. In one embodiment, two pairs of cantilevered leaf springs may be employed, with one pair on respective opposed sides of the trailer frame extending rearwardly thereof and the other pair, again on respective opposed sides of the trailer frame, extending forwardly thereof. This tandem arrangement provides a mirror image of the two pairs of springs, and associated axles, with respect to a generally vertical plane extending transversely of the trailer frame. Preferably, the one ends of the rearwardly and forwardly extending, cantileveral leaf springs which are connected to the trailer frame on each side thereof, are unitary with each other, such that the two leaf springs on each side of the frame can be provided as a single unit. Nevertheless, each leaf spring can act independently of the other. In this tandem arrangement and as discussed briefly above, the one end of each leaf spring may be connected rigidly, for example, by bolting, to the trailer frame. Such an arrangement is satisfactory if the trailer frame in use is fairly level and the road surfaces on which the trailer is used, are fairly smooth, as for typical road usage. If, however, the trailer frame needs to be angled and/or the trailer is used over cross-country conditions, the load distribution on the trailer axle(s) could well be uneven. Such a problem could be overcome by connecting the one end of each leaf spring pivotally to the trailer frame, either directly or indirectly via a sub-frame pivotally connected to the main trailer frame by a bush. In order that the invention may be more fully understood, preferred embodiments in accordance therewith will now be described by way of example and with reference to the accompanying drawings in which: Figures 1 and 2 are respective plan an side elevational views of a prior art trailer suspension; Figures 3 and 4 are respective plan and side elevational views of a first embodiment of trailer suspension in accordance with the present invention; Figure 5 is a graph of trailer loads against leaf spring deflections of the trailer suspensions shown in Figures 3 and 4, when compared against those parameters of the prior art trailer suspension shown in Figures 1 and 2; Figures 6 and 7 are respective plan and side elevational views of another embodiment of trailer suspension in accordance with the invention, with a tandem arrangement; Figure 8 is a side elevational view of an alternative arrangement for connecting suspension leaf springs to a trailer frame; Figures 9, 9 A and 10, 10A are respective side and front elevational views of two forms of securement of a leaf spring to a trailer axle; Figures 11 to 13 are respective side elevational views of additional means for securing a leaf spring to a trailer axle; Figures 14 to 16 are respective side elevational views of three forms of leaf spring end for securement to a trailer axle; Figures 17 to 19 are respective side elevational views of three different leaf springs each comprising a main leaf spring and an auxiliary leaf spring; - 1 ■ Figures 20 and 21 are respective side elevational views of two forms of auxiliary component for use with the trailer suspension of the invention; Figure 22 is a diagrammatic, partial front elevational view of a cranked arrangement for a trailer axle; Figure 23 is a side view of another form of leaf spring end for securement to a trailer axle; Figure 24 is a side elevational view of a modified form of the tandem arrangement shown in Figures 6 to 8; Figures 25 and 26 are respective side elevational views of further embodiments of tandem trailer suspension with auxiliary suspension means provided; Figure 27 is a side elevational view of a modified form of the suspension shown in Figure 25; Figures 28 and 29 are respective plan and side elevational views of a modified form of the trailer suspension shown in Figure 27; and Figures 30 and 31 are respective side elevational views of yet a further embodiment of trailer suspension, shown with the trailer in respective unladen and laden conditions. Referring firstly to " Figures 1 and 2 of the drawings, a prior art trailer partially shown at 1, comprises a frame 2 and a suspension including a pair of triple leaf springs 3 extending generally longitudinally of the frame 2 on respective opposed sides thereof. The front end 4 of each leaf spring 3 is connected to the frame 2 by means of a bracket 6 and a bush 7, whilst the rear end 5 of each leaf spring 3 is connected to the frame 2 by means of a bracket 8, shackle 9 and two bushes 10. An axle 11 is located transversely of the trailer frame 2 and is mounted at respective opposed ends 12 to the springs 3 generally centrally thereof by means of inverted U-bolts 13. A running wheel 14 is mounted to each end 12 of the axle 11. With this known arrangement, a compromise in the load to deflection stiffness ratio, namely, the spring rate, is involved and resides between a spring rate which is as soft as possible to provide the best isolation of the trailer frame and associated body (not shown) from rough road surfaces and a spring rate which is as stiff as possible for stability when the trailer is fully laden, particularly with a high centre of gravity load. For economic reasons, this compromise spring rate needs to be generally constant over the complete load range, that is to say, when the trailer is empty or unladen to bump inputs when fully laden. As a result, the isolation, or ride, of the trailer 1 when unladen tends to be very stiff and, therefore, undesirable. Also, to prevent the trailer axle 11 or wheels 14 contacting the trailer frame 2 during, say, bump inputs, the clearance therebetween has to be larger than is often desirable for access to the trailer and maintenance purposes. Referring now to Figures 3 and 4, a first embodiment of trailer suspension, indicated generally at 21, comprises a trailer frame 22 and a pair of single leaf springs 23 extending generally longitudinally of the frame 22 on respective opposed sides thereof. One end, in this case, the front end 24, of each leaf spring 23 is bolted, at 26 to the underside 28 of the trailer frame 22 in cantilever fashion, with the other end, in this case, the rear end 25, of each leaf spring 23, which would otherwise be free, being wrapped around, as shown at 27, and secured to ' a corresponding end 32 of an axle 31 extending tranversely of the trailer frame 22. A running wheel 34 is mounted to each end 32 of the axle 31. The wrapped round end 27 of each cantilevered spring 23 may be secured to the corresponding end 32 of the axle 31 by any suitable means. For example, and as discussed above, the wrapped-around other end 27 of each leaf spring 23 may be push-fitted, friction-fitted, adhered, puddle or full welded, bolted, clip-secured, clamp-secured to the end of the axle 32 or any combination thereof Such arrangements will be described in more detail hereinbelow. In this first inventive embodiment of trailer suspension 21, each leaf spring 23 can, in use, deflect sufficiently to contact progressively along its length the underside 28 of the trailer frame 22, as the trailer load increases from unladen to fully laden. This effectively reduces the working length of each leaf spring and, as a consequence, increases the stiffness or rate thereof. Also, as each leaf spring 23 contacts the underside 28 of the trailer frame 22, with a corresponding reduction in the effective working length of each leaf spring 23, the bending stress therein is reduced, thus allowing the use of much lighter leaf springs and, in this case, single leaf springs. Thus, there is provided a trailer suspension with an economic, variable leaf spring rate which provides good isolation from a road surface from the unladen to fully laden conditions, and beyond, of the trailer, to reduce any bump or overload deflection of the leaf springs 23. Turning now to Figure 5, here is shown a graph of a range of loads (lbs) versus the deflection (ins) of each leaf spring under those loads. The spring rate, sometimes known as the "isolation property" of the spring, is a tangent to the curve at any point. The leaf spring has a higher rate when the gradient of the tangent is higher, namely, is more steep. In the graph shown in Figure 5, the dashed line 41 represents load versus deflection for the conventional leaf spring arrangement described above with reference to Figures 1 and 2, whilst the full line 42 represents the load versus deflection for a leaf spring 23 of the first embodiment of trailer suspension 21 described above with reference to Figures 3 and 4. These two graphs are plotted for a trailer from unladen with no load to well above fully laden, the fully laden load being, in this particular case, 500 lbs. Thus, it can be seen that each spring 3, 23 of the conventionally and inventive trailer suspensions 1 and 21, have substantially the same spring rate at the fiilly laden (500 lbs) condition of the trailer. However, with the suspension 21 of the first embodiment of Figures 3 and 4, the rate of each cantilever spring 23 is much less than that of each conventional leaf spring 3, thereby providing a trailer suspension 21 which is much softer than the conventional suspension 1 at lighter trailer loads. Also, it can be seen from the graph of Figure 5 that the inventive embodiment of trainer suspension 21 has a much lower deflection, when absorbing bump inputs above the fully laden condition of the trailer, than that of the prior art suspension 1. This effect allows for a lower trailer frame height under fully laden conditions. Turning now to a second embodiment of trailer suspension, indicated generally at 51 in Figures 6 and 7, two pairs of cantilevered leaf springs 53, 63 are employed, with one pair 53 on respective opposed sides of a trailer frame 52 extending rearwardly thereof and the other pair 63, again on respective opposed sides of the trailer frame 52, extending forwardly thereof. This tandem arrangement provides a mirror image of the two pairs of cantilevered leaf springs 53,63, and associates axles 54,64, with respect to a generally vertical plain extending transversely of the trailer frame 52. In this tandem trailer suspension 51, one end, namely the front end 55 of each of the rearwardly extending cantilevered leaf springs 53 is connected rigidly by bolts 56 to the trailer frame 52. The other rear end 57 of each of the rearwardly extending leaf springs 53 is secured to the corresponding end 58 of the rear axle 54 by being wrapped therearound, as shown at 59. Similarly, the rear end 65 of each of the forwardly extending pair of leaf springs 63 is bolted, as shown at 66 to the underside 60 of the trailer frame 52, with the front end 67 of each of the pair of forwardly extending leaf springs 63 being secured to the corresponding end 68 of the front axle 64, by being wrapped therearound, as shown at 69. As indicated above, the ends 55, 65 of the two leaf springs 53, 63 on each side of the trailer frame 52 which are connected rigidly to the trailer frame 52, are formed integrally with each other. Nevertheless, each spring 53, 63 can act independently of the other. The wrapped-around ends 59,69 of each pair of rearwardly-extending and forwardly extending leaf springs 53,63 may be secured to the respective axle ends 58,68 by any suitable means, such as those discussed above in relation to the first embodiment of Figures 3 and 4. Running wheels 61 are mounted at respective ends 58,68 of the rear and front axles 54,64. This tandem arrangement for the second embodiment of trailer suspension 51, in which the ends 55,65 of the respective pairs of cantilevered leaf springs 53,63 are bolted , at 56,66, to the underside 60 of the trailer frame 52, is satisfactory if the trailer frame 52 is, in use, fairly level and the road surfaces on which the trailer is used, are fairly smooth, as for typical road usage. If, however, the trailer frame 52 needs to be angled and/or the trailer is used over cross-country conditions, the load distribution on the trailer axles 54,64 could well be uneven. Such a problem could be overcome by connecting the front ends 55 of the rearwardly extending pair of leaf springs 53 and the rear ends 65 of the forwardly extending leaf springs 63 to the trailer frame 52 by being bolted, at 56,66, to a sub-frame 62, which in turn, is pivotally mounted to the trailer frame 52 by a bush 70. As discussed above, the otherwise free, wrapped around ends 27, 59,69 of the cantilevered leaf springs 23,53,63 can be secured to their respective axle ends 32,58,68 by any suitable means, one example of such means being shown in Figures 9 and 9 A, wherein a puddle weld 70 is used to secure the wrapped around end 27,59,69 of each leaf spring 23,53,63 to the respective end 32,58,68 of the axle 31,54,64. The puddle weld 70 may be provided at any suitable position around the wrapped around end 27, 59, 69 of the spring 23, 53, 63. In Figure 10, the otherwise free end 25,57,67 of each leaf spring 23,53,63 is wrapped around, at 27,59,69, the end 32,58,68 of the corresponding axle and is secured thereto by a continuous weld 71. Alternatively, the weld 71 may extend partially around the wrapped around end 27, 59, 69 of each spring 23, 53, 63. Figure 12 shows another arrangement for securing the wrapped around end 27,59,69 of each leaf spring 23,53,63 to the corresponding end 32,58,68 of the axle, namely, a clip arrangement 72 comprising a lug 73 nested within a bent-over end portion 74 of the spring 23,53,63 and a plate 75, the retaining lug 73 having respective holes through which the arms of a securing U-bolt 76, engaging plate 75, is received. A similar clip is shown in Figure 13, wherein an eye clip 77 extends around the wrapped around end 27,59,69 of each leaf spring 23,53,63, with retaining clips 78 and securing bolts 79. The clip arrangements shown in Figures 12 and 13 increase the securement of the wrapped around leaf spring end 27,59,69 to the axle end 32,58,68 and are particularly useful for higher axle torques, such as those experienced during heavy breaking. These clipping arrangements are preferably used in addition to any previously-described securement, such as a friction fit or adhesive, between the wrapped around end of each cantilevered leaf spring and the axle. As shown in Figure 11, a bolt 80 could be received through in-register drillings passing through each axle end 32,58,68 and the wrapped around end 27,59,69 of each leaf spring 23, 53,63 for securement therebetween, in which case, the drillings and bolt 80 preferably pass through the neutral axis of the axle, in bending, to minimise the high stress concentrations created therein under service loadings. As the wrapped around ends 27,59,69 of the leaf springs 23,53, 63 use normal leaf spring eye manufacturing techniques , they could be constituted by any of the typical spring eyes used at present. For example, Figure 14 shows a typical downturned eye 81 as illustrated in Figures 3 to 13, Figure 15 shows a so-called "Berlin" eye 82, and Figures 16 shows at upturned eye 83 which could be used with a trailer having an abbreviated sub-frame 84. The embodiments of trailer suspension described above in relation to Figures 3 to 16 employ a simple, single leaf spring which is usually adequate for many light trailer applications. However, on heavier or more sensitive trailer applications, a single leaf spring may be inadequate, in which case, at least one additional, auxiliary leaf spring could be employed, for coping with heavier loads and to provide some friction to damp any suspension oscillations, without the need to add extra, external dampers or to provide further variable rate characteristics for the suspension. One such example is shown in Figure 17 and comprises a main, single leaf spring 91 with its otherwise free end 92 wrapped around the corresponding end of an axle (not shown) and an auxiliary upper leaf spring 93 extending partially along the length of the main leaf spring 91. A further example is shown in Figure 18 and comprises, again, a main, single leaf spring 91 with its otherwise free end 92 wrapped around the corresponding end of an axle (not shown). An additional, auxiliary upper leaf spring 94 extends along the length of the main leaf sprig 91 and has its free end 95 wrapped at least partially around the wrapped around end 92 of the main leaf spring 91. In this example the auxiliary upper spring 94 and its wrapped around end 95 provide a safety feature for preventing loss of control of the associated trailer, should the main leaf spring 91 fail. A further example is shown in Figure 19, comprising, once again, the main single leaf spring 91, with its otherwise free end 92 wrapped around an axle end (also not shown), and an auxiliary lower leaf spring 96 which extends partially along the length of the main leaf spring 91 but which is shaped, in this case, with an arcuate portion 97, to add friction to the suspension without effectively altering the operational characteristics of the main leaf spring 91. This shaped auxiliary leaf spring 96 pre-loads the main leaf spring 91, to damp any oscillations of the suspension without the need for extra, external dampers, and to provide further variable spring rate characteristics and rebound support for the suspension. As an alternative or in addition to adding an auxiliary leaf spring to increase the load capacity of the inventive trailer suspension, as shown in Figures 17 to 19, external additional springing could be employed. For example, and as shown in Figures 20, there is provided a pair (only one shown) of single cantilevered leaf springs 101 with their otherwise free ends 102 wrapped around an axle end 103, with three different positions for an additional, external spring, in this case, a polymer spring. In its first optional position, as shown at 104, the polymer spring acts directly on the leaf spring 101. In its second optional position 105, the polymer spring acts directly on the axle, whilst in its third optional position 106, the polymer spring acts upon a bracket 107 attached to the axle. As discussed, this additional springing is provided by a polymer spring, although other spring media can be employed, for example, coil, air, leaf, rubber or mixed polymers. In Figure 21 there is shown another modified form of inventive trailer suspension for tuning the rate versus load characteristic thereof, wherein there comprises a trailer frame 110 and a pair (only one shown) of cantilevered single leaf springs 111, as discussed above, with a tapered member 112 secured to the underside 113 of the frame 110. That spring rate versus load characteristic modifying member 112 may be solid or flexible, as required. In use, and when the load on the trailer increases, the cantilevered single leaf spring 111 engages the member 112, to modify the spring rate. If the member 112 is made of a soft medium, then it could be shaped and dimensioned to make permanent contact with the leaf spring 111, to prevent stones and other undesirable items from being caught between the leaf spring 111 and underside 113 of the trailer frame 110, which would otherwise cause damage or change the operating characteristics of the suspension. The axles of light trailers tend to be constructed by securing spindles to the opposed ends of hollow tubes, in which case, the suspensions can be mounted to either the spindles or the tubes, to suit the particular installation. The tubes, or other fabricated centre sections, of the axles may be cranked to lower or raise those centre sections to suit particular trailer constructions. Alternatively, the axle end spindles can be cranked. In these arrangements, the otherwise free ends of the cantilevered leaf springs can be mounted to either the cranked ends of the centre sections of the axles or to the cranked spindles. In Figure 22, there is shown alternative examples of such a cranked arrangement, which comprises an axle, indicated generally at 115, with a lower central section 116 having an upwardly cranked end section 117 and an upper spindle 118 to which a running wheel 119 is mounted. In one alternative, the otherwise free, wrapped around end 121 of a cantilevered leaf spring is secured to the lower central section 116 of the axle 115, whilst in the other alternative, the otherwise free wrapped around end 122 of a cantilevered leaf spring is secured around the spindle 118. In the inventive embodiments described above, all the otherwise free, wrapped around ends of the leaf springs of the suspensions have been wrapped around axles of circular cross-section, although axles of other cross-sections may be used, for example, those with square cross-sections. In such cases, the otherwise free end of each leaf spring can be suitable shaped to wrap around squared sectioned axles, such as that as shown in Figure 23, wherein the leaf spring 123 has its otherwise free end 124 configured to wrap around a square cross-sectioned axle end (not shown). Such a configuration increases the rigidity of securement of the leaf spring 123 to the axle end. In the embodiment discussed above with reference to Figure 8, there is shown a tandem arrangement of two pairs of cantilevered leaf springs 53,63 pivotally connected at their respective forward and rear ends 55,65 to a trailer frame 52 by means of a bush 70, the otherwise free, wrapped around ends 59,69 of the respective pairs of leaf springs 53,63 being in the form of downturned eyes. In Figure 24, those wrapped around ends 159,169 are in the form of upturned eyes, with respective front and rear ends 155,165 of the rearwardly and forwardly extending leaf springs 153,163 being bolted to a sub-frame 162 pivotally connected to the trailer frame (not shown) by a bush 170. Similar upturned eye configurations are shown in Figures 25 and 26. In Figure 25, the bracket 162 and bush 170 arrangement of Figure 24 connecting the respective front and rear ends 155,165 of the cantilevered leaf springs 153,163 to the trailer frame is replaced by an air spring 180 connected to the trailer frame 200, whilst in Figure 26, that bracket 162 and bush 170 arrangement is replaced by a polymer spring 190 again connected to the trailer frame 200. It is to be appreciated that any other additional springing medium could be used, for example, a coil spring or , as discussed above, an auxiliary leaf spring. In Figures 25 and 26, the air spring 180 and polymer spring 190 provide no effective lateral location for the suspension with respect to the trailer frame 200. Modifications to resolve this lack of lateral support are described below with reference to Figures 27 to 29. In Figure 27, there is shown a modified embodiment of trailer suspension in accordance with the invention, which is similar to that described above with reference to Figure 25. In this further embodiment of trailer suspension, as indicated generally at 201, a tandem arrangement with respective pairs of rear and front cantilevered single leaf springs 253, 263, have their respective front and rear ends 255,265 bolted, at 266 to an air spring 280. The otherwise free ends 259,269 are wrapped around opposed ends 254,264 of respective rear and front transverse axles 254,264, in the form of upturned eyes. Again, the front and rear ends 255,265 of the leaf springs 253, 263 are formed integrally with each other. An auxiliary front leaf spring 270 has one end 271 connected to the trailer frame, in cantilever fashion, 280 by means of a bush 272. The otherwise free end 273 of the cantilevered auxiliary front leaf spring 270 is secured to the front axle 264 by means of a bracket 274. However, at the otherwise free, other end of the rear cantilevered leaf spring 253, there is provided a rear auxiliary leaf spring 290 whose rear end 291 is also connected to the trailer frame in cantilever fashion via a shackle 292 which allows for any effective length change of the suspension 201 during use. The front end 293 is connected to the rear axle by a bracket 294. An shown in Figure 27, the respective front and rear ends 293,273 of the rear and front cantilevered auxiliary springs 290,270 are attached to their corresponding axles by flat-faced brackets 294,274. However, such attachment may be effected by wrapping those otherwise free ends 293,273 of the rear and front cantilevered auxiliary springs 290,270 around the corresponding axles, as shown in Figures 28 and 29. Here, this modified embodiment of trailer suspension, as indicated generally at 301 comprises, in tandem, a pair (only one shown) of cantilevered rear leaf springs 302, each having its front end connected to an air spring 320, similar to that arrangement shown in Figures 25 and 27. The otherwise free , rear end 303 of each leaf spring 302 is wrapped around and secured to the corresponding end region of the rear trailer axle 304. Similarly, a pair (only one shown) of cantilevered front leaf springs 305 each has it rear end connected to the air spring 320, with its otherwise free, front end wrapped around and secured to the front trailer axle 307. Each of a pair (only one shown) of auxiliary front leaf springs 308 has its front end 309 bolted to the trailer frame 310, in cantilever fashion, with its otherwise free rear end 311 wrapped around and secured to the front axle 307, * outboard of the front leaf spring 305. Each of a pair (only one shown) of cantilevered auxiliary rear leaf springs 312 has its otherwise free front end 313 wrapped around and secured to the rear axle 304, outboard of the rear leaf spring 302. The rear end 314 of each auxiliary rear leaf spring 312 is connected to the frame 310 for sliding movement with respect thereto in the longitudinal direction of the frame 310. A transverse location bracket 315 is provided at the rear end 314 of each spring 312, to locate each spring 312 transversely of the frame 310. A running wheel 316 (only two shown) is mounted to the end of each axle 304,307, with the clearance between the inner side of each wheel 316 and the outer side of the air spring 320 being indicated as x. Several advantages are associated with the embodiment of tandem trailer suspension show in Figures 28 and 29, namely: 1. Only one additional spring, such as an air spring 320, is required at each side of the trailer frame 310 to support two axles 304,307; 2. If air springs 320 are used, then they normally leave their centres offset inboard of the longitudinal axis of the outboard leaf springs 308,312. This is because air springs 320 are normally wider than those leaf springs 308,312 and the outside edges of the air springs 320 have to clear the inside of the running wheels 316, such clearance being, in this case, x. Thus, no special brackets or transversely bent leaves are required to support fully the air springs 320. With the embodiment of Figures 28 and 29, the inboard, cantilevered leaf springs 302,305 can be positioned to suit accommodation of the air springs 320, or indeed any other type of additional springing, with the transverse locations of the outboard cantilevered leaf springs 308, 312 being as far outboard as possible for trailer stability; and 3. The tandem axle transverse type scrubbing loads can be spread over a wide span of the trailer frame. If the trailer frame needs to be higher than the mountings of the pair(s) of "cantilevered leaf springs on opposed side of the frame; then those springs can be arranged to engage progressively against a secondary spring, as shown in Figures 30 and 31. Here, the suspension 401 is mounted downwardly of the trailer frame 402. Each cantilevered main leaf spring 403 has one end 404 bolted at 405 to the frame 402, with one end 406 of a secondary leaf spring 407 and a spacer block 408 located therebetween. The other, free end 409 of the secondary leaf spring 407 is in contact with the underside 410 of the frame 402. As the load on the trailer increases, each main leaf spring 403 engages progressively along the length of its secondary leaf spring 407 and transfers the load through that secondary leaf spring 407 into the frame 402. This arrangement has several advantages. For example, because each secondary leaf spring 407 is flexible, the spring rate of each main leaf spring 403 is modified in a gradual manner. Also, the end 409 of each secondary leaf spring 407 slides along the underside 410 of the frame, thus adding some friction therebetween to dampen the suspension 401. It is to be appreciated that certain features of the invention which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub- combination.

Claims: CLAIMS 1. A trailer comprising a frame and a pair of leaf springs extending longitudinally of the frame on respective opposed sides thereof, wherein each leaf spring is cantilevered with one end connected to the frame and with its otherwise free, other end secured to an axle of the trailer. 2. A trailer according to claim 1, wherein the axle is a single axle extending transversely of the frame of the trailer. 3. A trailer according to claim 1, wherein the otherwise free, other ends of the leaf springs are secured to respective opposed ends of the trailer axle. 4. A trailer according to claim 1, wherein the axle of the trailer comprises a pair of stub axles on respective opposed sides of the trailer frame. 5. A trailer according to claim 4, wherein the otherwise free, other ends of the leaf springs are secured to respective stub axles. 6. A trailer according to claim 1, wherein each leaf spring is a single leaf spring. 7. A trailer according to claim 1, wherein the otherwise free end of each leaf spring is secured to the trailer axle by being wrapped therearound. 8. A trailer according to claim 1, wherein the one end of each leaf spring which is connected to the trailer frame, is connected rigidly thereto. 9. A trailer according to claim 1, wherein the one end of each leaf spring which is connected to the trailer frame, is connected pivotally thereto. 10. A trailer according to claim 7, wherein the other end of each leaf spring which is wrapped around the trailer axle, is secured thereto by means of a push-fit, a friction fit, adhesive, a puddle weld, a continuous weld, a bolt, a clip or any combination thereof. 11. A trailer according to claim 7, wherein the other end of each leaf spring which is wrapped around the trailer axle, is secured thereto by a bolt passing through a hole extending through the axle and leaf spring. 12. A trailer according to claim 1, wherein each leaf spring is, in use, arranged to contact the trailer frame directly as the load of the trailer increases, to reduce the effective working length of each leaf spring and, as a consequence, to increase the rate of the spring. 13. A trailer according to claim 1, wherein each leaf spring is, in use, arranged to contact the trailer frame indirectly as the load of the trailer increases, to reduce the effective working length of each leaf spring and, as a consequence, to increase the rate of the spring. 14. A trailer according to claim 13, wherein each leaf spring is, in use, arranged to contact a member attached to the trailer frame, to reduce the effective working length of each leaf spring. 15. A trailer according to claim 14, wherein the member is rigid. 16. A trailer according to claim 14, wherein the member is resilient. 17. A trailer according to claim 16, wherein the resilient member extends between the underside of the trailer frame and the associated leaf spring. 18. A trailer according to claim 6, wherein each single leaf spring has an additional, auxiliary leaf spring arranged to pre-load the single leaf spring, to prevent, or at least substantially reduce, deflections of the single leaf spring which are otherwise too high between unladen and fully laden conditions of the trailer. 19. A trailer according to claim 18, wherein each auxiliary leaf spring has one end connected to the trailer frame adjacent the one end of the corresponding single leaf spring and which extends at least partially along the length of the single leaf spring. 20. A trailer according to claim 19, wherein the other end of each single leaf spring is wrapped around the trailer axle and each auxiliary leaf spring extends along the length of the corresponding single leaf spring and has its other end at least partially wrapped around the wrapped around other end of the corresponding single leaf spring. 21. A trailer according to claim 18, wherein each auxiliary leaf spring has its other, free end bearing against the underside of the corresponding single leaf spring. 22. A trailer according to claim 18, wherein each auxiliary leaf spring has its other, free end bearing against the trailer frame. 23. A trailer according to claim 22, wherein each auxiliary leaf spring extends 24. A trailer according to claim 1 comprising two pairs of cantilevered leaf springs of which one pair on respective opposed sides of the trailer frame extends rearwardly thereof and the other pair on respective opposed sides of the trailer frame extend forwardly thereof. 25. A trailer according to claim 24, wherein the one ends of the rearwardly and forwardly extending, cantilevered leaf springs which are connected to the trailer frame on each side thereof, are unitary with each other, such that the rearwardly and forwardly extending leaf springs on each side of the frame constitute a single unit. 26. A trailer according to claim 24, wherein the one ends of the cantilevered leaf springs are connected rigidly to the frame. 27. A trailer according to claim 24, wherein the one ends of the cantilevered leaf springs are connected pivotally to the frame. 28. A trailer according to claim 24, wherein the one end of each of the cantilevered leaf springs is connected to the frame via an additional springing medium. 29. A trailer according to claim 28, wherein said additional springing medium is an air spring, coil spring, polymer spring, or leaf spring. 30. A trailer according to claim 28 further comprising two pair of auxiliary leaf springs with the leaf springs of each pair of auxiliary leaf springs being on respective opposed sides of the frame, with one end of each auxiliary leaf spring respective opposed sides of the frame, with one end of each auxiliary leaf spring being connected to the frame in cantilever fashion and with the other end of each auxiliary leaf spring being secured to the corresponding axle. 31. A trailer according to claim 30, wherein one pair of auxiliary leaf springs extends rearwardly of the trailer with the other ends of said rearwardly-extending, auxiliary leaf springs connected to a front axle of the trailer and wherein the other pair of auxiliary leaf springs extends forwardly of the trailer with the other ends of said forwardly-extending, auxiliary leaf springs connected to a rear axle of the trailer. 32. A trailer according to claim 31, wherein the other ends of the leaf springs of each pair of rearwardly and forwardly-extending, auxiliary leaf springs which are connected to respective front and rear axles, are connected thereto by being wrapped therearound. 33. A trailer according to claim 30, wherein the one end of each leaf spring of one of the pairs of auxiliary leaf springs is connected to the frame in sliding frictional engagement therewith. 34. A trailer according to claim 28, wherein the one end of each leaf spring of at least one of the pairs of auxiliary leaf springs is connected to the frame by a bracket to locate said at least one pair of auxiliary leaf springs transversely of the frame. 35. A trailer according to claim 31, wherein the one end of each of the pair of forwardly extending, auxiliary leaf springs is connected to the frame by a bracket to locate said at least one pair of auxiliary leaf springs transversely of the frame. 36. A trailer according to claim 33, wherein the one end of each leaf spring of said one pair of auxiliary leaf springs is connected to the frame by a bracket to locate said one pair of auxiliary leaf springs transversely of the frame. 37. A suspension for use with a trailer, comprising a pair of leaf springs arranged to extend longitudinally of a frame of a trailer on respective opposed sides thereof, wherein one end of each leaf spring is arranged to be connected to the frame in cantilever fashion and the otherwise free, other end of each leaf spring is arranged to be secured to an axle. 38. A suspension according to claim 37, wherein the otherwise free, other end of each leaf spring is arranged to be secured to a single axle extending transversely of the frame of a trailer. 39. A suspension according to claim 37, wherein the otherwise free, other ends of the leaf springs are arranged to be secured to respective opposed ends of a trailer axle. 40. A suspension according to claim 37, wherein the otherwise free, other ends of the leaf springs are arranged to be secured to respective ones of a pair of stub axles on respective opposed sides of a trailer frame. 41. A suspension according to claim 37, wherein each leaf spring is a single leaf spring. 42. A suspension according to claim 37, wherein the otherwise free end of each leaf spring is arranged to be secured to a trailer axle by being wrapped therearound. 43. A suspension according to claim 37, wherein the one end of each leaf spring is arranged to be connected rigidly to a trailer frame. 44. A suspension according to claim 37, wherein the one end of each leaf springs is arranged to be connected pivotally to a trailer frame. 45. A suspension according to claim 42, wherein the other end of each leaf spring which is arranged to be wrapped around a trailer axle, is arranged to be secured thereto by means of a push-fit, a friction fit, adhesive, a puddle weld, a continuous weld, a bolt, a clip or any combination thereof. 46. A suspension according to claim 42, wherein the other end of each leaf spring which is arranged to be wrapped around a trailer axle, is arranged to be secured thereto by a bolt arranged to pass through a hole extending through the axle and leaf spring. 47. A suspension according to claim 37, wherein each leaf spring is arranged to contact a trailer frame directly, as the load on the trailer increases, to reduce the effective working length of each leaf spring and, as a consequence, to increase the rate of the spring during use. 48. A suspension according to claim 37, wherein each leaf spring is arranged to contact a trailer frame indirectly as the load on the trailer increases, to reduce the effective working length of each leaf spring and, as a consequence, to increase the rate of the spring during use. 49. A suspension according to claim 48, wherein each leaf spring is arranged to contact a member attached to trailer frame, to reduce the effective working length 49. A suspension according to claim 48, wherein each leaf spring is arranged to contact a member attached to trailer frame, to reduce the effective working length of each leaf spring during use. 50. A suspension according to claim 41, wherein each single leaf spring has an additional, auxiliary leaf spring arranged to pre-load the single leaf spring, to prevent, or at least substantially reduce, deflections of the single leaf spring which are otherwise too high between unladen and fiilly laden conditions of a trailer during use. 51. A suspension according to claim 50, wherein each auxiliary leaf spring has one end arranged to be connected to a trailer frame adjacent the one end of the corresponding single leaf spring and at least partially extends along the length of the single leaf spring. 52. A suspension according to claim 51, wherein the other end of each single leaf spring is arranged to be wrapped around a trailer axle and each auxiliary leaf spring extends along the length of the corresponding single leaf spring and has its other end at least partially wrapped around the wrapped around other end of the corresponding single leaf spring. 53. A suspension according to claim 50, wherein each auxiliary leaf spring has its other, free end arranged to bear against the underside of the corresponding single leaf spring in use. 54. A suspension according to claim 50, wherein each auxiliary leaf spring has its other, free end arranged to bear against a trailer frame in use. spring. 56. A suspension according to claim 37, comprising two pairs of cantilevered leaf springs of which one pair is arranged to extend on respective opposed sides of a trailer frame rearwardly thereof and the other pair is arranged to extend on respective opposed sides of the trailer frame forwardly thereof. 57. A suspension according to claim 56, wherein the one ends of the rearwardly and forwardly extending, cantilevered leaf springs which are connectable to a trailer frame on each side thereof, are unitary with each other, such that they constitute a single unit. 58. A suspension according to claim 56, wherein the one ends of the leaf springs are arranged to be connected rigidly to a trailer frame. 59. A suspension according to claim 56, wherein the one ends of the leaf springs are arranged to be connected pivotally to the frame. 60. A suspension according to claim 56, wherein the one end of each of the leaf springs is arranged to be connected to a trailer frame via an additional springing medium of the suspension. 61. A suspension according to claim 60, wherein said additional springing medium is an air spring, coil spring, polymer spring, or leaf spring. 62. A suspension according to claim 60 further comprising two pair of auxiliary leaf springs with the leaf springs of each pair of auxiliary leaf springs arranged to be on respective opposed sides of a frame, with one end of each auxiliary leaf spring leaf springs with the leaf springs of each pair of auxiliary leaf springs arranged to be on respective opposed sides of a frame, with one end of each auxiliary leaf spring arranged to be connected to the frame in cantilever fashion and with the other end of each auxiliary leaf spring arranged to be secured to a corresponding axle. 63. A suspension according to claim 62, wherein one pair of auxiliary leaf springs is arranged to extend rearwardly of a trailer frame with the other ends of said rearwardly-extending, auxiliary leaf spring arranged to be connected to a front axle of a trailer and wherein the other pair of auxiliary leaf springs is arranged to extend forwardly of the trailer with the other ends of said forwardly-extending, auxiliary leaf springs arranged to be connected to a rear axle of a trailer. 64. A suspension according to claim 63, wherein the other ends of the leaf springs of each pair of auxiliary leaf springs which are arranged to be connected to respective front and rear axles, are connectable thereto by being wrapped therearound. 65. A suspension according to claim 62, wherein the one end of each leaf spring of one of the pairs of auxiliary leaf springs is arranged to be connected to a trailer frame in sliding frictional engagement therewith. 66. A suspension according to claim 60, wherein the one end of each leaf spring of at least one of the pairs of auxiliary leaf springs is arranged to be connected to a trailer frame by a bracket, to locate said at least one pair of auxiliary leaf springs transversely of the frame. 67. A suspension according to claim 63, wherein the one end of each of the pair of forwardly extending auxiliary leaf springs is arranged to be connected to a trailer frame by a bracket, to locate said at least one pair of auxiliary leaf springs transversely thereof 68. A suspension according to claim 65, wherein the one end of each leaf spring of said one pair of auxiliary leaf springs is arranged to be connected to a trailer frame by a bracket to locate said one pair of auxiliary leaf springs transversely thereof. 69. In combination, a suspension according to claim 37 and an axle to which the otherwise free, other end of each leaf spring is secured. 70. In combination, a suspension according to claim 56 and a pair of axles wherein the otherwise free, other ends of the two pairs of cantilevered leaf springs are secured to respective ones of the axles.

Inventors: GLASS MICHAEL F, MOELLER DAVID N, GLASS, MICHAEL, F., MOELLER, DAVID, N.
Applicants: DETROIT STEEL PRODUCTS CO INC, GLASS MICHAEL F, MOELLER DAVID N, DETROIT STEEL PRODUCTS CO., INC., GLASS, MICHAEL, F., MOELLER, DAVID, N.
Application year: 2000
Main classification: B60G11
IPC codes: B60G3, B60G5, B60G9, B60G11