The invention relates to a center axle trailer ar rangement for heavy-duty road transports according to the preamble of an independent claim directed there to.

In heavy-duty road transports, it is known to use a center axle trailer capable of being coupled to a towing vehicle, such as a truck, and including a rigid towbar and wheel axles , along with their wheels , fixedly present usually in the middle part of a trailer in a direction transverse to a lengthwise di rection of the trailer. In addition, the opposite ends of such trailers are often provided with lifting legs for resting the trailer against a support sur face when uncoupled from the tractor unit .

Advantages of a center axle trailer include its ex cellent cornering as it follows closely the path of a tractor unit, without the adverse tendency to " short - cutting" , and its simple design . A drawback of the discussed trailer, on the other hand, is its poor stability, especially in a combination made up of two or more center axle trailers . Since the convention 1 center axle trailer transmits, by way of its rigid towbar , some loading also onto the tractor unit, the allowable load-bearing capacity of such a combination has been restricted with current regulations .

In the above-stated purpose , it is further known to employ a semi- trailer, which is coupled by its front end rotatably onto the top of a tractor unit's frame . The semi- trailer has its rear end provided with its own wheel axles along with their wheels . A benefit of the semi-trailer is its simple design, by virtue of which it is in practice the most common combination in heavy-duty road transports because a fifth wheel to be placed on top of the tractor unit' s frame is affordable in price and, being standardized to a great extent , enables cross -couplings, i.e. any semitrailer can be pulled by almost any tractor unit .

However , it is the fifth wheel -gooseneck assembly, used in coupling a semi-trailer to a tractor unit , which makes the semi-trailer' s frame structure quite high, reducing the load capacity of cargo space and raising the center of gravity. It is particularly due to the lack of a lengthwise joint that the traction of a tractor unit varies from side to side as the semi- trailer is tilting. Therefore, it is known in traction-requiring transports to implement the coupling of a semi- trailer and a tractor unit with a so- called universal joint table, which nevertheless in practice further increases the height of the semi trailer' s frame structure .

In terms of coupling semi- trailers for so-called HCT (High Capacity Truck) combinations there are two techniques, the first being such that a second semi trailer is raised onto a fifth wheel placed on top of a rear section of the first semi-trailer . The second option is such that to the tail of a semi-trailer is coupled a second semi-trailer by means of an auxilia ry cart or so-called dolly. The whole consisting of a dolly and a semi- trailer can also be referred to as an actual trailer or full trailer regardless of whether the dolly is coupled to the semi-trailer type actual frame member by means of a fifth wheel or a ball ring. As for the above-mentioned options , a drawback with the first coupling is a very high frame height of the trailer, i . e . a poor load capacity, and a drawback with the latter is respectively its poor stability.

In the above purpose there is further employed a full trailer, i.e. a so-called actual trailer, with a typ ical feature of including an articulated (non load transmitting) towbar , and a dolly capable of turning along with the towbar and having rotatably attached thereto a gooseneck present at a front end of the full trailer' s frame structure . The full trailer' s frame structure has its other end provided with a rear axle or axle assembly, which is non- swinging and/or swinging in response to the action of e.g. friction- controlled wheel axles .

The full trailer offers a benefit of being able to bear its own load, by virtue of which its load- bearing capacity need not be technically restricted. On the other hand, the transport combination based on this type of trailer has a drawback of being in its lengthwise direction so-called multiaxially double- articulated, which is why it is considerably less stable than for example a semi- trailer . The succes sive coupling of e.g. two full trailers makes the discussed assembly quad-articulated and thereby even more unstable . In practice, pulling two or more full trailers is so unstable that, as a rule, the use of such combinations is not allowed among passenger traffic . Because of a gooseneck, used in the coupling of a full trailer to a tractor unit, the full trailer' s frame structure is clearly higher than e.g. that of a center axle trailer, thereby reducing a load capacity, especially in countries where the total height of a trailer is limited, which is quite common.

It is by integrating a fifth wheel -equipped dolly, commonly used in the coupling of a tractor unit and a trailer, and a semi-trailer that a trailer-matching combination is obtained. However, such a dolly must include brakes and tail lights, which is why dollies in certain purposes are unnecessarily "equipped" . In addition, the dolly is coupled to a tractor unit typically fitted with a tow coupler, whereby the tow coupler must be further approved for the purpose at hand since the dolly' s towbar is fixed as opposed to the bar of a full trailer .

It is further known in the foregoing context to employ friction- controlled swinging wheel axles , along with their wheels , which improve handling of the transport combination and reduce considerably tire wear and fuel consumption. The dolly equipped with a friction- controlled wheel axle steers itself better in curves and follows almost identically the path o a tractor unit . Hence, the lateral forces generated in tires are also distributed equally amongst all wheel axles,· in a tri-axle trailer, for example, every wheel axle has considerably less lateral forces ap- plied to the tire, whereby the service kilometers for a front axle increase by as much as 50% and for a rear axle by as much as 70% .

It is by virtue of toothed king pin brackets that the friction- controlled wheel axles typically feature an automatic return of steering and a load-dependent stabilization of steering. Thus, the discussed wheel axle does not require an external return of steering, hence reducing the number of components needed therein and the weight of wheel axles . The friction- controlled wheel axles are further typically provided with a steering lock device, which prevents tires from turning when reversing and improves the combination' s stability when the driving speed increases be yond a legal speed per hour established for the locking.

By means of a center axle trailer arrangement according to the present invention, intended for heavy-duty road transports , it is possible to provide a decisive improvement regarding the foregoing problems and to thereby upgrade essentially the available prior art . In order to attain this objective, the center axle trailer arrangement of the invention is principally characterized by what is presented in the characterizing clause of an independent claim directed thereto.

The most significant benefits gained by a center axle trailer arrangement of the invention, intended for heavy-duty road transports , should be mentioned to include the simplicity and efficiency of its con- struction and operation as it enables, on the one hand, an integration of the good maneuverability and simple design of a center axle trailer and, on the other hand, the good load-bearing capacity of a full trailer, which is attainable by simply utilizing a towbar, included in the center axle trailer and ro tatable around a horizontal axis , i.e. in a so-called uniaxial manner, and wheel axles , along with their wheels on the opposite sides of the frame structure, present at the opposite ends of the center axle trailer and swinging around a vertical axis .

The center axle trailer arrangement of the invention is equal to a full trailer as it has just as good a load-bearing capacity and it works without transmitting a vertical load, yet which, by virtue of its good maneuverabi1ity, follows the tractor unit more closely than a full trailer . The invention makes also possible more than 30 -meter long combinations permitted by HCT (High Capacity Truck) regulations without requiring changes to road infrastrueture for example in intersections and roundabouts , etc .

It is by virtue of the arrangement according to the invention that the frame structure of a center axle trailer included therein need not be provided with e.g. a gooseneck, nor with a steerable dolly, by virtue of which it is possible to implement the trailer' s frame height to be substantially lower and the load capacity to be higher than e.g. in semi- or full trailers . Therefore, neither is there any need to provide the center axle trailer with lifting legs connected to its frame structure as the swinging ax- les can be positioned in such a way that the trailer keeps its balance in a lengthwise direction without lifting legs .

It has been confirmed on the basis of preliminary studies and computationa1 analyses that the center axle trailer arrangement of the invention is even es sentially more stable than full trailer combinations of similar length.

The invention further provides a possibility of standardization and cross-coupling, i . e . the coupling of exactly identical center axle trailers successive ly in a manner most appropriate for a given purpose and by using a necessary number of trailers .

The invention makes further possible the endeavors of trailer superstructure manufacturers towards stand ardization as the arrangement of center axle trailers according to the invention is excellently applicable to increasing transport combinations' length/capacity (25,5 m - _> 34 , 5 m) , to be implemented for example in Finland, in such a way that the transport combination consists of e.g. three cargo space modules of equal length.

Accordingly, the invention provides a significant im provement regarding the logistics of heavy-duty transport as it enables particularly the length and load-bearing capacity of transport combinations to be increased without needing structural modifications of road infrastructure , which is hugely significant in terms of national economy. Other preferred embodiments for a center axle trailer arrangement of the invention are presented in dependent claims directed thereto .

In the following specification, the invention will be described in detail with reference to the accompany ing drawings , in which fig . 1 shows , in an exemplary perspective view, one preferred center axle trailer included in a center axle trailer arrangement of the invention, fig. 2 shows one preferred center axle trailer ar rangement of the invention consistent with HCT regulations in a side view, a top view, and in a top view with the center axle trailer arrangement in cornering motion, figs. 3A-3E show further a few preferred center axle trailer options, included in a center axle trailer arrangement of the invention, in side views and in top views, fig. 4 shows the cornering motion of two center axle trailer arrangements of the invention in a roundabout (R 25 m) , and fig. 5 shows a few exemplary superstructures for center axle trailers included in a center axle trailer arrangement of the invention.

The invention relates to a center axle trailer arrangement for heavy-duty road transports , which has an elongated frame structure 1 for a load to be carried, one or more wheel axles 2 in a lengthwise direction s in its middle section provided with wheels 3 present on each side of the frame structure and, from the standpoint of manufacturing costs, most preferably in the lengthwise direction, and which has a towbar 4 and/or its coupling element 4 ' at one or each end of the frame structure for transmitting force between the center axle trailer and a vehicle 5, such as a truck and/or another trailer, coupled thereto . As presented by way of example especially in fig. 1 , the center axle trailer K is provided with a towbar 4 rotatable uniaxially around a horizontal axis for transmitting a substantially horizontal force between the center axle trailer and a vehicle 5, such as a truck and/or another trailer, coupled thereto . In addition, the center axle trailer K has one or each end thereof provided with one or more wheel axles 2a along with their steerable w wheels 3a on the opposite sides of the frame structure .

In a preferred embodiment for a center axle trailer arrangement of the invention, referring to what is displayed in figs . 1 , 2 and 3A-3E, at least one end of the center axle trailer K is provided with one or more friction- controllably swinging wheel axle assemblies 2a successive in a lengthwise direction s, along with their steerable wheels 3a on the opposite sides of the frame structure .

In a further preferred embodiment for a center axle trailer arrangement of the invention, referring specifically e.g. to fig . 1 , the center axle trailer K included therein has the opposite ends of its frame structure 1 provided with one or more friction- controlled wheel axle assemblies 2a successive in a lengthwise direction s, along with their wheels 3a on the opposite sides of the frame structure .

In a further preferred embodiment of the invention, referring to figs . 2, 4 and 5, the center axle trailer arrangement includes at least two center axle trailers K of equal length, coupled to each other with a towbar 4 and provided with a wheel axle assembly 2a along with its wheels 3a on the opposite sides of the frame structure . In reference to what is pre sented in fig. 5 , the center axle trailer arrangement of the invention, by virtue of its simple basic con struction and by making use of appropriate super structures, is applicable to indeed a wide variety of transport services .

It is for a better illustration of the invention that from the center axle trailer shown in fig . 1 have been omitted per se conventional structural elements included in the trailer, such as a suspension, the frame structure' s intermediate beams, etc. In the exemplary embodiments depicted in figs . 3A-3E, some of the trailers have steerable wheels 3a both at front and rear ends (figs . 3B and 3C) and some only at a front or rear end (figs . 3A, 3D and 3E) . The embodi- ment of fig. 3A is provided with steerable wheels 3a on two successive wheel axles 2a, and further in figs . 3A and 3E there are non-steerable wheels 3b at a front or rear end, while the trailer of fig . 3D has a rear section with no "extra wheels" at all in addi tion to middle wheels 3.

In this regard, in a further preferred embodiment , referring specifically e.g. to fig. 5 , the center axle trailer arrangement includes at least three center axle trailers K of equal length, coupled to each other with a towbar 4 and provided with a wheel axle assembly 2a along with its wheels 3a on the opposite sides of the frame structure .

In a further preferred embodiment , referring specifi cally to fig. 1, the center axle trailer K, included in the center axle trailer arrangement , is provided not with e.g. a friction-controlled wheel axle assembly but , instead, with an assembly Z, such as e.g. an axle lightening assembly or the like, reducing the friction which opposes swinging of the wheel axle assembly 2a. The discussed assembly Z comprises mechanical , electric and/or pneumatic actuators for reduc ing the friction of the wheel axle assembly' s 2a wheels 3a with respect to the ground .

In view of manufacturing costs and adjustability, the lightening assembly Z is in practice implemented e.g. with actuators controlling the pressure of a pneumat- ic or hydraulic suspension of the wheel axle assembly 2a .

In a further preferred embodiment of the invention, referring specifically e.g. to figs . 2, 4 and 5 , the center axle trailer arrangement of the invention, and the vehicle 5 pulling the same, have an overall length L which essentially complies with a maximum length designated for a vehicle combination, such as that consistent with HCT (High Capacity Truck) regulations, which will be 34, 5 meters e.g. in Finland.

In this regard, there is illustrated in fig . 4 a mu tual comparison relating to the cornering motion of two optional center axle trailer arrangements of in vention in a roundabout (R 25 m) : in the left hand side embodiment , the last two wheel axles of trailers are self-steering (which enables almost unlimited in crease of the transport combination' s length, approx imately 46 m in the embodiment shown in this figure) , while in the right hand side embodiment , respective ly, only the first and last wheel axles are self- steering. The point illustrated in the figure is that increasing the length of transport combinations does not in itself bring about needs for modifications in road infrastructure .

It is obvious that the invention is not limited to the above-described or -explained embodiments but can be varied within the basic inventive concept in a multitude of ways, depending each time on logistic requirements and e.g. on country-specific regulations . Accordingly, it is obvious that a center axle trailer of the invention can be used as a member of prior known combinations, i.e. a trailer of the in vention can be coupled to the rear of e.g. a semitrailer or full trailer combination. On the other hand, it is possible that to the rear of a combination according to the invention be coupled, e.g. by means of a dolly, a semi-trailer or an actual trail- er. Furthermore , as opposed to e.g. conventional wheel axles friction-steerable with so-called kingpins, it is also possible to utilize other types of similar axle structures .