The present invention relates to a trailer for transporting an object such as a boat, comprising a chassis supported by wheels, wherein sets of wheels comprising one or more wheels are each connected pivotally to the chassis by means of a connecting arm.

Boats are regularly transported out of the water and transported overland, for instance for the purpose of maintenance, repairs or other work, such as having a (pre-purchase) inspection carried out or transport to a winter storage.

A trailer of the type stated in the preamble is known in the field. An example hereof is the Netherlands patent NL191884 which protects a trailer in which the chassis is adjustable in the height relative to the ground surface and adjustable in the width. For this purpose the known trailer is provided at the rear with two pivotable connecting arms, one on each side, on which a wheel set with two wheels is mounted in each case. The known trailer is intended as slipway and transport trailer for respectively taking a boat out of and placing it in the water and for transporting a boat.

The known trailer does however have a limited loading capacity, which is largely determined by the support of the chassis by the sets of wheels.

Other embodiments of the type of trailer stated in the preamble are also known in practice, these being provided with two connecting arms with their own wheel set, which are pivotally connected to the chassis and move apart during displacement from a rest position to a transport position. Such an embodiment as known in practice is for instance described in the American patent application

US2008/247850. These known embodiments have the drawback that the centre-to- centre distance between the wheels increases in the transport position relative to the rest position. This has an adverse effect on the overland travel characteristics of the trailer. A great deal of friction occurs particularly in bends, as a result of which the construction is subjected to great forces and the tyres undergo much wear.

The invention has for its object to provide a trailer of the type stated in the preamble which obviates the above stated drawbacks. The trailer according to the invention has for this purpose the feature that each set of wheels is connected to the chassis by means of two connecting arms, the connecting arms each being pivotally connected to the chassis at one proximal outer end and being pivotally connected to the one or more sets of wheels at the other, distal outer end.

The trailer according to the invention has the advantage that it is supported at multiple positions on the rear side of the chassis at the position of the proximal outer ends of the connecting arms, whereby the loading capacity increases considerably. Owing to the connection of the distal outer ends of the two connecting arms to the one or more sets of wheels, the centre-to-centre distance moreover remains the same in all positions in the case of two or more wheel sets, as a result of which less friction results in the bends so that the construction and the tyres are less badly affected.

The Japanese patent application JP59179412 describes a trailer according to the preamble of claim 1 , wherein each set of wheels is connected by means of four connecting arms to the chassis, the connecting arms each being slidably connected to the chassis at one proximal outer end and pivotally connected to the one or more sets of wheels at the other, distal outer end. The connecting arms form a parallelogram construction which is movable by means of a drive body which acts directly on the distal outer end of the connecting arms at the position of the pivotable connection to the set of wheels. The vehicle according to JP59179412 has a complex construction with many moving parts and a height which is adjustable to limited extent and which is determined by the width of grooves in which the proximal outer ends of the connecting arms are movably received and by the stroke of the cylinder forming the drive body.

The international patent application W097/48572 describes a trailer according to the preamble of claim 1 , wherein each set of wheels is connected by means of two connecting arms to the chassis, the connecting arms each being pivotally connected to the chassis at one proximal outer end and pivotally connected to the one or more sets of wheels at the other, distal outer end, with the proviso that W097/48572 does not have connecting arms but connecting elements of a generally triangular form. Each connecting element is movable by means of an associated drive body. For good operation of the height adjustment in the transport vehicle according to W097/48572 it is necessary for the control of the two drive bodies to be coupled, which makes the height adjustment complex.

The trailer according to the invention has the further feature that the connecting arms are mutually connected at the proximal outer ends thereof by means of at least one drive body, which is adapted to move the proximal outer ends in order to increase the distance between the one or more sets of wheels and the chassis.

The trailer according to the invention hereby provides a height adjustment with a relatively large height range with a minimal number of moving parts.

In a first preferred embodiment of the trailer according to the invention the two connecting arms are connected pivotally to each other at the distal outer ends thereof by means of a lever, on which lever the one or more sets of wheels are mounted. Applying a lever at the distal outer ends of the connecting arms makes it possible to accommodate the connecting arms in very compact manner under the chassis in the rest position of the trailer. A minimum height can hereby be set between the underside of the chassis and the road surface in the rest position. According to a further preferred embodiment, the sets of wheels are coupled in pairwise manner by means of a tandem, the tandem being mounted on the lever. Applying a tandem on the lever enables a plurality of sets of wheels to be mounted on the lever at a mutual centre-to-centre distance to be predetermined. In another preferred embodiment of the trailer according to the invention the length of the first connecting arm roughly corresponds to the length of the second connecting arm. When the connecting arms extend, the sets of wheels mounted on the lever will take up the most central possible position under the chassis. The sets of wheels support the chassis optimally in this central position and thereby enable a maximum loading capacity. According to yet another preferred embodiment, at the distal outer end the first connecting arm has a general S-shape, the dimensions of which correspond roughly to the length of the lever. Owing to the pivotable connections between the first connecting arm, the lever and the second connecting arm, in combination with the dimensions of the lever and the distal outer end of the first connecting arm, the lever can fold over and be received under the chassis parallel to the distal outer end of the first connecting arm. This enhances the intended compact folded-away position in the rest position of the trailer. The drive body preferably comprises a hydraulic cylinder. A hydraulic cylinder can be connected in simple manner to the hydraulic system generally present on any suitable tractive vehicle for the trailer.

In a self-propelling embodiment the trailer is provided with means for independent movement.

The invention will now be described in more detail with reference to the figures. The same components are designated in the figures with the same reference numerals.

Figure 1 shows a schematic view of a first preferred embodiment of a trailer according to the present invention; Figure 2 shows a side view with partly broken-away parts of the rear part of the trailer of figure 1 ;

Figure 3 shows the rear part of figure 2 in the highest position; Figure 4 shows a schematic side view of a part of the rear part of figure 3;

Figure 5 shows a schematic view of a second preferred embodiment of a trailer according to the present invention; Figure 6 shows a side view with partly broken-away parts of the rear part of the trailer of figure 5.

In all figures the same components are designated with the same reference numerals.

Figure 1 shows a first preferred embodiment of a trailer 1 according to the invention. Trailer 1 is intended for the purpose of transporting a boat. To this end the trailer comprises a chassis 2 which is generally U-shaped. Chassis 2 comprises two longitudinal beams 3 which are mutually connected at one outer end by means of a transverse beam 4. Chassis 2 is further provided with two drawbars 5 provided at their outer end with a joint drawbar eye 6. Chassis 2 is supported on its rear part by wheels 10. Longitudinal beams 3 are each provided here with a housing 7 on which boat supports 8 are arranged. Chassis 2 can preferably be adjusted in both the length and the width by means of techniques known in the field. Reference is made for instance to the above stated Netherlands patent NL191884. Figure 2 shows a side view of the rear part of chassis 2, in which wheels 10 are in their lowest position or rest position. Figure 2 is drawn to scale. Figure 3 shows the same view of wheels 10 in the highest position or transport position. Components are omitted in figures 2 and 3 for the sake of clarity, including a part of housing 7 and the two outer wheels 10. According to the invention wheels 10 are connected pivotally to chassis 2 by means of a plurality of connecting arms. Figure 4 shows a schematic view of these connecting arms and the two sets of wheels as part of the trailer of figure 3.

In the shown first preferred embodiment wheels 10 form part of two double sets of wheels which are mutually coupled by means of a tandem 14. Each double wheel set consists of two wheels 10 which are mounted on a shared wheel shaft 17.

A first connecting arm 11 is pivotally connected to chassis 2 at the position of pivot point S1. A second connecting arm 12 is pivotally connected to chassis 2 at the position of pivot point S2. Pivot points S1 and S2 are each situated at the proximal outer end of respective connecting arms 11 and 12. Connecting arm 11 is pivotally connected at the other "distal" outer end to the "distal" outer end of connecting arm 12 by means of a pivot point S3. The connection between connecting arms 11 and 12 takes place by means of a third connecting arm 13. Connecting arm 13 is pivotally connected at the one outer end to the "distal" outer end of connecting arm 11 at the position of pivot point S3. At the other outer end connecting arm 13 is pivotally connected to the "distal" outer end of connecting arm 12 at pivot point S4. Tandem 14 is mounted on a pivot point S5 located roughly in the centre of connecting arm 13 between pivot points S3 and S4.

The height of wheels 10 relative to chassis 2 can now be set by moving connecting arms 11 and 12. For this purpose connecting arms 11 and 12 are mutually connected at the proximal outer ends thereof by means of at least one drive body which is adapted to move the proximal outer ends toward each other in order to increase the distance between the wheels and the chassis. In the shown first preferred embodiment the drive body is a cylinder 15 with a piston rod 16. Cylinder 15 is connected to the proximal outer end of connecting arm 12 by means of pivot point S7 while the outer end of piston rod 16 is pivotally connected to the proximal outer end of connecting arm 11 at the position of pivot point S6. Cylinder 15 is preferably a hydraulic cylinder so that it can be connected to the hydraulic system of the tractive vehicle for energizing thereof.

Connecting arms 11 , 12 and 13 have dimensions and forms such that in the lowest position of trailer 1 they are folded up beneath chassis 2 and take up minimal space there. In the highest position of trailer 1 the connecting arms are extended and take up maximal space, and determine the distance of wheels 10 relative to chassis 2.

Three parts, each of a distinct form, can be discerned in connecting arm 11. Part 11 A tapers from pivot points S1 and S6. Part 11 B runs straight and lies at an angle relative to part 11 A. Connecting arm 11 then has a further part 11C which is per se straight, but is connected at an angle to part 11 B. Parts 11 A, 11 B and 11 C define a gentle S-bend.

Two parts, each of a distinct form, can be discerned in connecting arm 12. Parts 11A and 12A are very similar in form. Part 12A tapers from pivot points S2 and S7. Part 12B runs straight and extends approximately in line with part 12A.

Connecting arm 13 has a generally straight form. During movement of connecting arms 11 and 12 connecting arm 13 fulfils the function of lever. In the lowest position of trailer 1 the connecting arms 11 and 12 extend toward each other substantially parallel to the underside of chassis 2. In this lowest position connecting arm 13 extends roughly parallel to part 11 B and is as it were taken up into the gentle S- bend of parts 11C, 11B and 11A.

Figures 5 and figure 6 show a second preferred embodiment of the trailer according to the invention. Figure 5 shows a schematic view of trailer 100 and figure 6 shows a side view, with partly broken-away parts, of the rear part of trailer 100 of figure 5.

The second preferred embodiment is very similar to the first preferred embodiment. The most important difference is formed by the number of sets of wheels. In the second preferred embodiment wheels 10 form part of four double wheel sets which are mutually coupled by means of a tandem 114. Each double set of wheels consists of two wheels 10 which are mounted on a shared wheel shaft 17. Tandem 114 is mounted on pivot point S5 situated roughly in the centre of connecting arm 13, between pivot points S3 and S4. The double wheel sets are coupled in pairwise manner to each other by means of a coupling part 118. Coupling parts 118 of each pair of wheel sets are pivotally connected to tandem 114 at the position of pivot points S108 and S109.

The sets of wheels can of course also number other than two or four, or the sets of wheels can take a single-wheel form as desired. When one set of wheels is applied, the shaft of the double set of wheels can be mounted directly on connecting arm 13. The present invention is of course not limited to the shown and described preferred embodiments. In addition to use for transporting boats, the trailer according to the invention is for instance highly suitable for transporting other objects. It is possible here to envisage for instance heavy construction elements such as concrete elements.

The scope of protection sought therefore extends to any embodiment falling within the text of the claims, as seen in the light of the foregoing description and accompanying drawings.