The present invention relates to a human force driven cart suspension. We define the term human force driven cart as a light cart or similar, arranged for being pulled by a person, wherein the weight of the cart itself is comparable with the weight of the load to be carried by the cart. More specifically, it relates to a suspension mechanism for the wheel axles for a bicycle trailer or child carriage. The suspension mechanism is arranged for being adjusted depending on the size of the load's mass, i e. weight.

Background art

The size of the load's weight may, for a bicycle trailer or a child carriage vary considerably compared to the cart's own weight. Thus the suspension properties for the suspension mechanism hardly be adjusted to an average weight of the most probably occurring load. If a bicycle trailer weighs 15 kg and has a suspension mechanism arranged for this weight plus a load of up to 20 kg, such a suspension mechanism will incur much jumping over uneven ground if the actual load is e.g. a small child weighing 5 kg. This as opposed to e.g. the conditions for a person car, its weight likely being 1500 kg, while the driver's and the accompanying passengers' weight may vary between 50 and 300 kg without significantly affecting the vehicle's properties.

Among the prior art exists US-patent US6764082B2 which has a leaf spring suspension comprising a small stack of leaf springs with a clamp for varying the free length of the leaf spring, and an axle retainer at the end of the leaf spring. There are several single components such as clamps, screws, springs, spring clamps, spring clamp tensioner screws, spring- to axle bracket screws, and axle bracket, in such an assembled suspension mechanism, so the patented model depends on several serially connected components shall withstand vibrations and loads. There are several components which may incur a total breakdown.

Brief summary

The invention is defined in the independent patent claim Drawing figures

The invention is illustrated in embodiments in the enclosed drawings. The invention is a perspective view aslant from above and slightly from the rear, of a suspension device according to the invention, and there is indicated by broken lines that it may be sled in and attached in a frame of a bicycle trailer or a child cart, preferably one at either side of the cart, in the right and left frame rail. The pivot arm (2) is provided with a sleeve-shaped axle bracket (3) for a wheel axle in its one end and pivots about a bracket axle (4) at its opposite end, and is dampened by resilient rods (5) which ride with their lateral surfaces against an athwart suspending bolt (7). In the illustrated embodiment the resilient rods (5) are of equal lengths. The springs may be formed of a composite material such as GRP rods or spring steel, and the remainder in aluminium or steel according to the mechanical designer's desire. The suspending bolt may in the illustrated embodiment be moved between the holes (71 ) until a desired length of the resilient springs ride on it so as for obtaining a desired stiffness in the suspension.

Fig. 2a is a rear end view of the suspension device. We here see forwardly in the direction of the cart frame Here is shown an approximate end view of the resilient rods (5) in contact under the athwart contact bolt (7), and in the lowest part is shown the axle bracket (3) in an end view of the pivot arm (2). The bracket axle is omitted in this drawing just for clarity.

Fig. 2b is the opposite end view of the suspension mechanism. We see the end (21 ) of the pivot arm (2), view of the protruding ends of the bracket axle (4) and some liners between those. Also shown is the end of a damper arm (8) arranged between the base bracket (1 ) and the pivot arm (2). The damper arm may be attached in its first end in the base bracket's plate portion (11 ) and in its second end in the pivot arm, by the spring bracket (6), please see Fig. 4. In this manner also the damper arm is protected by the base bracket (1 ) and the pivot arm (2), which in an embodiment fills out the width of the base bracket.

Fig. 2c is a side elevation view of the spring suspension (1 ) shown in Fig. 1.

Fig 2d is a bottom view, and Fig. 2e is a top view of the same.

Fig. 3 is a perspective view of the spring suspension according to the invention, seen aslant and from below in the front. A clean, smooth and non-vulnerable surface of the pivot arm (2) and the flange walls (12, 13) is exposed to grinding, impacts and shocks from below, and the axle bracket (3) shall hold a wheel axle, either with a separately oscillating wheel or with a common axle, depending on the desire of the mechanical designer. The pivot arm protects the resilient rods from impacts and grinding, a practical feature particularly when using GRP rods. Also the direction. The spring suspension is robust as such, not vulnerable and torsion stable as it utilizes the full width of the frame rail.

Fig. 4a is a vertical length section through the spring suspension according to the invention and illustrates, together with Fig. 4b, its action. In unloaded position the axle bracket (3) is held in neutral position by the damper arm (8) which is flexible, but which does not have a spring constant of any significance. The one or the several resilient rods (5) is/are kept unloaded onto the contact bolt (7) which in this image resides in the remotest holes (71 ) from the bracket axle (4) which is the common pivot point for the pivot arm with the resilient rods.

Fig. 4b illustrates a loaded position for the pivot arm (2) wherein a large length of the resilient rods (5) is shown in loaded, bent state by a force FWG (wheel / ground) from a wheel axle and held by a force FL from a loaded carriage, and wherein one may expect that the mechanism is just about to bottom in itself. The position for the contact bolt shown here will provide the softest resilience. If the contact bolt is moved to the holes (71 ) further to the left, the resilience will be more rigid, and be suitable for a larger load.

Fig. 5 shows a bottom view of the spring suspension partially cut through the middle portion of the pivot arm (2), wherein this alternative embodiment of the invention illustrates three resilient rods (5L, 5M, 5K) of different lengths so as for them to extend to a contact bolt (7) which may be inserted through different bolt holes (71 a, 7ab, 71 c) which are remotest from, closer to, and closest to the bracket axle (4). In the illustrated embodiment only the longest resilient rod (5L) will engage onto a contact bolt when said contact bolt (7) resides in the holes (71 a), and progressively further rods be engaged when the contact bolt (7) is moved to holes (71 b, 71 c) further to the left, i.e. forwardly on the suspension mechanism.

Embodiments of the invention

The invention is in the shown embodiments a bicycle trailer or child cart wheel suspension mechanism comprising a base bracket (1 ) for mounting on the bicycle trailer's or child cart's main frame (0), wherein the base bracket (1 ) comprises a mainly horizontal pivot arm (2) on a generally horizontal athwart oriented bracket axle (4) in the first end (21 ) of the pivot arm, and with a generally horizontal, athwart axle bracket (3) in the second, opposite end (22) of the pivot arm, with one or more resilient rods (5) mounted in a spring bracket (6) on the pivot arm (2) and which extend generally radially in the direction out from the bracket axle (4), an athwart contact bolt (7) in the base bracket (1 ) for the one or more resilient rods (5) arranged to let them bend against when the pivot arm's axle bracket (3) is loaded by a vertical force, wherein the athwart contact bolt (7) is arranged to be placed in a desired radial distance from the athwart bracket axle (4). The base bracket may be cut from an extruded aluminium profile and rounded off in the lower fore edges of the lateral walls. In embodiments of the inventions one may have one, two, three or more resilient rods (5). The rods may be made in composite material or from spring steel, and they may in a practical embodiment be set in close fit borings, cemented or not, in the spring bracket (6). The resilient rods (5) may in an embodiment of the invention be replaceable for repair or modification of the spring force. The resilient rods may be formed from so-called GRP rod, which are stainless, or spring steel rods, leaf spring steel of straight or decreasing width. The pivot arm (2) with its parallel bores for the bracket axle (4) and the wheel axle in the axle bracket (3) may be formed from an extruded profile or moulding. It may be formed in aluminium, steel or even plastic or fibre composite. The bolts (4, 7) may be made in steel, aluminium, or other suitable material. Liners may be made in steel, bronze, plastic, Teflon or other suitable material, and the entire mechanism may be lubricated or dry

The purpose of enabling selecting the position for the contact bolt (7) is to vary the working length of the one or more resilient rods (5), and thus the oscillation properties of the entire spring suspension. A short working length of the spring (5) provides a higher spring force than a long working length of the spring (5).

In an alternative embodiment shown in Fig. 5 the athwart contact bolt (7) is arranged to be placed in a desired radial distance from the athwart bracket axle (4). This alternative allows to move the contact bolt so as for enabling it to progressively come in engagement with two, three or more parallelly mounted springs (5L, 5M, 5K) of different length and one or more contact bolts 7 arranged for being pushed in depending on how many springs (5L, 5M, 5K) one wishes to have an active engagement against, and thus a progressively increasing spring force is achieved

In an embodiment of the invention the base bracket (1) comprises a U-shaped main rail with top plate (1 1 ) and longitudinally extending lateral walls (12, 13), and wherein the bracket axle (4) and the contact bolt (7) runs through contact bolt holes (71 ) through the lateral walls (12, 13).

In an embodiment of the wheel suspension mechanism the pivot arm (2) and the one or more resilient rods (5) extend with a small mutual angle, mainly in the same horizontal direction, from the bracket axle (4). This provides a compact spring suspension which does not occupy much of the length of the right and left frame portion, respectively, of a bicycle trailer or a child cart, and it also provides a protection for the resilient rods (5) which from below are covered by the pivot arm (2) and laterally by the lateral walls (12, 13) of the base bracket (1 ).

In an alternative, longer extending embodiment of the invention the resilient rods extend in the opposite direction of the bracket axle (4) relative to the pivot arm (2). This requires further that the holes (71 a, 71 b, 71 c) in the base bracket (1 ) also are formed to the opposite side relative to the bracket axle (4) and that the length of the mechanism nearly doubles, ant that the pivot arm (2) no longer covers the resilient rods (5). But such an embodiment is feasible

In an embodiment of the wheel suspension mechanism the top plate (1 1 ) of the base bracket (1 ) comprises longitudinally extending profile rails (14) arranged to be sled into corresponding track rails (15) in the main frame (0), and latches for keeping it all in place longitudinally, please see Fig. 1.

In an embodiment of the invention, please see particularly Fig. 4, a hold- and damper arm (8) is arranged between the base bracket and the pivot arm (2).

Advantages of the invention

The base bracket with its belonging components form a compact wheel suspension mechanism A U-shaped base bracket is easy to manufacture from an extruded profile with longitudinal flanges (14) and arranged for being sled into place in corresponding longitudinally extending grooves (15) of an extruded profile, e.g. aluminium profile. The base bracket may be attached with a screw or bolt and may not be laterally displaced when first mounted. It is easily replaceable, easily retrofitted, and probably cheaply manufactured.