document: FIELD OF THE INVENTION 
       The present invention relates to a sulky comprising two wheels, individually fastened, but located along the same rotational axis, to a common frame provided with a driver&#39;s seat and shafts leading towards the draught animal. 
       DESCRIPTION OF RELEVANT ART 
       Sulkies of this type are used for trotting races and the most important requirements are that they have a lightweight construction, that they are easy-running, and that they are strongly built to endure the specific strain during excercise and competitions. 
       To obtain constructions of a sufficiently stiff and stable structure and at the same time of lowest possible weight, sulkies so far have been manufactured as welded steel constructions as this has led to the most lightweight construction combined with sufficient strength. 
       Certainly there have earlier been attempts to build sulkies of aluminium, however such sulkies have got a rather bad reputation due to poor strength qualities. 
       A conventional sulky has its shafts fastened approximately 10 cms inside of the wheels. This fact leads to a construction well adapted for welded steel pipes, but it is unsuitable when light metals are used because the construction then requires welding. This is probably the reason why earlier attempts using aluminium have failed, as the design then has been similar to the conventional steel constructions requiring a welding process. It is a fact that aluminium and other light metals are difficult to weld, in particular weaknesses in the metal can not be allowed at, or close to, the welding points. 
       Storing and transportation of conventional sulkies has led to difficulties due to the sulkies having an awkward shape. The manufacturing process has also been expensive and much handwork has been required. Sulkies having even less weight have always been desirable, even if specialists in this field of technique have been convinced that still lighter sulkies could not be manufactured without a corresponding strength reduction. 
       SUMMARY OF THE INVENTION 
       The object of the present invention is to provide a new sulky construction having such a design that it may be manufactured of light metal and other lightweight and yet durable materials. 
       A further object of the present invention is to provide a sulky which may be assembled easily by a user himself, from substantially flat elements requiring only a small space during storage and transportation, said elements being easily dispatched in a flat package. 
       Still a further object of the present invention is to build up a sulky from inexpensive semi-produced components as casted elements and extruded profiles. 
       Still a further object of the present invention is to provide a sulky having a stable construction as the shafts as well as the crossbar transfer substantially all the load to the wheel planes only. 
       Finally it may be mentioned that an object of the present invention is to provide a sulky which easily may be assembled by the user himself by means of ordinary hand tool, and where all the connections become secure, without any play, even if the single components are produced with ordinary manufacturing tolerances. 
       It should be mentioned that the new sulky construction having shafts fastened to the frame in the planes of the wheels results in the possibility of avoiding the traditional manual manufacturing process including welding of each individual sulky and instead using casting and mass production with corresponding low expenses. By changing to a casting process many of the details required in connection with the wheel suspension, the fastening of the shafts and the crossbar to the frame, may be integrated in the casting process without any additional expenditures. A design of the end frames as stated in connection with the present invention is also required to obtain a structure being well suited for box packaging and do-it-yourself kits based on simple threaded connections. 
       There is also obtained a weight reduction of approximately 40% for the complete sulky which has a total weight of approximately 18 kg in a ready-to-use state. 
       Finally it should be mentioned that a sulky according to the present invention in particular is designed to be colored by applying color tapes in all recesses of the profiles, a solution which leads to an inexpensive and individual color display system important for the end users. 
      
      
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To give a clear understanding of the present invention reference is made to the detailed description of an embodiment given below, and to the accompanying drawings in which: 
       FIG. 1 illustrates a side view of a sulky according to the present invention, 
       FIG. 2 illustrates a top view of a sulky according to FIG. 1, 
       FIG. 3 illustrates a cross section of the crossbar at the connection to an end frame, 
       FIGS. 4A-4C show an end frame in more detail, and 
       FIG. 5 shows how a dismantled sulky may be arranged in a flat package. 
      
      
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       In all of the Figures the same reference numbers are used for components having the same function, when appropriate. 
       In FIG. 1 the sulky 1 is shown in a side view, and it may be seen that both the wheel 2 and the shaft 3 are mounted to the end frame 5. 
       When FIG. 2, which shows the same sulky as in FIG. 1, but now seen from above, is compared with FIG. 1, where the same reference numbers are used, it may be seen that the driver&#39;s seat 4 is arranged centrally on the crossbar 6 which is fastened to the mounting bushings 7 in the end frames 5. 
       In FIG. 2 the foot treads 8 fastened to the shafts 3 also are shown, and FIG. 2 in particular shows how the end frames are shaped so that the wheel-fastening, shaft-fastening and crossbar-fastening devices all are arranged in the same vertical plane. This is important to obtain a best possible load situation. 
       As shown in FIGS. 1 and 2 the end frames 5 are arranged symmetrically related to the plane of the wheels 2. This leads to a stable construction of the sulky, but differs from conventional solutions. It may also be understood from FIGS. 1 and 2 that the crossbar 6 is adapted to the mounting bushings 7 and may be fastened thereto. An example of the assembly of those joints is described in more detail below. The details of these joints are important to obtain a stable and rigid frame which may resist the strain occuring during use, and this may be obtained without demanding requirements on the materials in these components or to the manufacturing tolerances of same. According to a preferred embodiment of the present invention the end frames 5, preferably of aluminium or a similar light metal, are casted, e.g. by means of a chill-casting or press-casting process using a light metal, or alternatively by producing the frames of reinforced plastics while the crossbar 6 may be manufactured of extruded aluminium or a similar light metal. Despite the inexpensive process and easily workable materials the geometric design leads to a stable and reliable construction. 
       The wheels may be fastened to a fork section 9 of the end frames 5 by means of conventional fastening technique, and in a similar manner the shafts 3, which may be made of light metal or plastics reinforced e.g. by carbon fibers, may be fastened to the end frames 5 by means of horizontally arranged fastening bolts 16 and further fastening screws 17 arranged in corresponding holes in the shaft 3. Thereby a fastening of the shaft so as to be adjustable in a longitudinal direction is obtained. 
       Finally it may be mentioned that the driver&#39;s seat 4 is fastened to the crossbar 6 by means of extruded brackets 12 which, if required, may be clamped thereto by means of conventional clamping devices comprising screws or bolts. 
       The crossbar 6 and the fastening of the same in one of the mounting bushings 7, is shown in more detail at the cross section illustrated in FIG. 3. The crossbar may be designed as an extruded aluminium profile 13 having a closed cross section with internal extending protrusions 14 and 15. In addition there are strengthening elements 18, 19 adapted to fit in with friction between the protrusions 14 and 15. Centrally in these strengthening elements threaded holes 20 and 21 are arranged, and the strengthening elements may be shifted along the aluminum profile 13 to a suitable place so that the threaded holes 20 and 21 coincide with the assembling recesses in the profile 13 and the mounting bushing 7. It may be noted that the strengthening elements 18, 19, arranged on diametrically and opposite faces of the aluminium profile 13, may be combined in one common integrated part as they may be designed, for example as a U-shaped or O-shaped bracket which may be shifted within the track made up of the protrusions 14 and 15. The material of the strengthening elements 18 and 19 may be stainless steel or a similar material having a higher rigidity than the material of the extruded profile 13. 
       In FIG. 3 one of the mounting bushings 7 is shown together with through screws 22 adapted for fastening the crossbar 6 to the mounting bushing 7. In this connection it is important that the manufacturing tolerances during extruding and casting allow easy introduction of the extruded profile 13 in the mounting bushing 7 with suitable play, however, in such a manner that the materials have a flexibility and deformability adapted so that when the screws 22 are tightened, the extruded profile and mounting bushing 7 will be pulled together by the strengthening elements 18 and 19 respectively, and possibly between oppositely arranged, external strengthening washers 23. After this tightening process the surfaces of the crossbar 6 and the mounting bushing 7 have been somewhat deformed, and therefore an exact adaptation is obtained. It should also be noted that outside the mounting bushing 7 there may also be placed strengthening washers 23, possibly counter bored in the bushing wall so that the material of the bushing 7 and the material of the extruded profile 13 are squeezed between element 19 and a washer of non-corrosive material 23, respectively, and are forcibly pressed towards the rigid bushing 7. Even if the manufacturing tolerances of the extruded profile and the bushing initially left some mutual play, the tightening of the bolt 22 deforms the material so that a close and durable connection is obtained. This connection method ensures a stable and reliable assembly using very simple means. 
       In FIGS. 4A-4C still more details of the end frame 5 are shown. Here the cross sections of the different parts of the frame also are illustrated. It may in particular be mentioned that the mounting bushing 7 has a cross section that with a certain play is adapted to the external section of the extruded aluminium profile which constitutes the crossbar 6 and is shown in FIG. 3. The loads are evenly distributed due to the symmetrical design of the end frames relative to the wheel planes, and this fact also contributes to a reliable solution in spite of the simple mounting process. The end frame has such a design that it may be cast in a tool comprising only one core and two side walls. The core may be pulled out vertically in a downward direction on the drawing, while all the side elements are bent out to slip the casted element, and the inside and outside of the mounting bushing 7 are formed in contact with the side elements. 
       The right and the left end frames are preferably casted in the same tool and are therefore quite identical when casted. The tool expenses therefore are reduced and also the storing charges as the number of spare parts also are reduced. In the shown embodiment the external part of the mounting bushing 7 is removed from opposite sides of the end frames before the assembly process, and the resulting holes are covered by caps. However, the invention comprises embodiments where the two end frames are maintained identical also after assembly. 
       If the qualities of the material and the cross section so allow, the central parts of the crossbar, i.e. the region where the bending moment reaches its maximum value during use, may be reinforced by introducing a square profile between the protrusions 14 and 15. 
       An important advantage of the present invention is that the complete sulky may be packed into a flat box for storing and transportation to distributers. The user may then buy the sulky as a construction kit and mount the parts himself in a quarter of an hour and then obtain a reliable and professional sulky having a lower total weight but with user qualities equal to those of traditional sulkies. It should also be mentioned that the end frames 5 are identical during production and thus freely may be used on the right or the left side of the sulky. The protruding part of the mounting bushing 7 may then be removed by a simple cutting process before assembly.
summary: Sulky comprising two wheels individually fastened along the same rotational axis, to a common structure provided with a driver&#39;s seat (4) and shafts (3) leading towards the draught animal. The sulky (1) consists of a construction kit comprising a plurality of substantially flat elements (2, 3, 4, 5, 6) adapted to be assembled by the end user by means of ordinary hand tools. Two of these parts are end frames (5) adapted for fastening of a wheel (2), a shaft (3), and the crossbar (6) in the same vertical plane.