Description

Technical Field

This invention relates to a load-bearing structural arrangement preferably for a vehicle, comprising a closed outer member defining an inner space and an inner member arranged in the inner space of the outer member.

Background Art

There is an element in the frame structure of the superstructure of buses that acts as connection between the floorboard or the chassis and the roof structure along the section delimited by the front and the rear panels, respectively. This is known by several names. In the present writing, I will call it also "bracket" due to its form.

In intercity and tourist buses, the bracket - apart from supporting the roof - has a most important role: passenger safety. In these buses, this function goes well beyond that of simple support, since in the event of any accident, the passengers' "residual space" must be secured by these components. However, here the load bearing on the roof is infinitesimal.

In the event of sideways overturn, brackets must absorb sufficient energy to prevent that the kinetic energy of the bus - determined by the speed, the mass and the centre of gravity of the bus - should cause such deformation in the superstructure as would make it extend into the residual space and hence put the life of the passengers at danger.

Of course, this can be solved also by monumental, oversized components or by excessively solid materials, but there are significant constraints to that.

The primary feature is the mass of the bus. The smaller the mass, the smaller the environmental load of the bus, i.e. its emission of pollutants, emission of noise and its impact on the road. Moreover, the problem outlined above is a self-amplifying one for, for a bus of a bigger mass travelling at the same speed, the amount of energy to be absorbed in case of accident is also be bigger, that is, the mass ought to be increased further and this can only end in a major compromise.

The second constraint is that of the purchase and maintenance costs. Materials that are much more solid than steel, but nevertheless light, are known, but they are most expensive. Even manufacturers known as major market actors use such materials to a limited extent only due to their price. Keen market competition makes it imperative to take into account the interests of the buyer, and the sale price is the first step there. The two biggest cost items of the operator are the purchase price and the cost of fuels consumed during usage. If these two are excessive, then he will either have to give up part of his profits, or raise his prices and have less work. Obviously, neither is desirable, so an interim solution implying safety for the passenger and a low cost ratio for the operator needs to be found.

In addition to the above, pursuant to the new EU directive, superstructure tests must be made not with the unladen mass of the bus, but with the expected maximum working load.

Since the risk of a sideways overturn is infinitesimal for low-floor buses, they are not tested for that. The superstructure of city buses with alternative drive systems and of the partly automotive trolley buses is packed completely, both from the top and from the bottom. On the side of the passenger space, there are pneumatic, electronic and electrical controls, valves, air reservoirs etc. On the external part of the superstructure, there are batteries, capacitors, drive containers, for trolley buses the current collector, for fuel cell drivers hydrogen containers, the fuel cell and some smaller or larger equipment. Depending on the size and type of the bus, this means a - dynamic - roof load of 1.6 to 4 tons that the traditional frame structures can only bear with the compromises made for tourist buses, and any reinforcements may trigger the same vicious circle. Attaining the appropriate efficient range meets with extraordinary difficulties.

US 6,378,933 Bl discloses a reinforced vehicle frame, wherein the tubular elements constituting the frame are reinforced so that a further three-dimensional core element and rigid foam are incorporated into their inner space. During rigidifying, the foam being introduced fixes the three- dimensional spatial core element constituting the inner member in the position it occupies, and at the same time also connects it to the tubular element constituting the outer member. This structural arrangement grants the structure greater mechanical strength than would an equipment made up of the tubular profiles constituting the outer member, but in case of big, concentrated force impacts, it cannot protect the outer member, i.e. the vehicle frame, from excessive defor- mation. The solution emphasises that, if possible, the rigid spatial body, that is, the inner member should have no contact anywhere with the outer member constituting the vehicle frame and applies to that effect, where appropriate, spacers to be fixed in advance by a separate work operation or after the positioning of the inner member, said spacers ensuring that the inner member that is not specifically fixed to them, only supported by them, should be located, as far as possi- ble, concentrically, in the middle. Thus the forces being generated will travel from the outer member (not including the spacers, if any) to the inner member exclusively through the rigid foam material until the outer member gets in touch, through its deformation, with the inner member. This solution cannot make the frame structure more loadable and more solid considering the currently known solution, hence for example in the vehicle industry, representing a tar- get area, it cannot be used preferably as bracket for buses, railway wagons etc. US 7, 114,763 B2 discloses an energy management system for use in a vehicle frame, wherein internal elements of various forms and sizes arranged in an element that can be regarded as an outer member are permanently fixed in their position and connected to the outer member by synthetic raisin during manufacturing. The primary goal of this solution is to absorb the forces impacting on the structural arrangement through the inner members partly flexibly and partly by deformation, which requires such geometrical dimensions as cannot be applied economically and technically as vehicle bracket in the target areas considered by us.

EP 0893331 Al discloses a reinforced structural member comprising a structural member defining a channel and a reinforcement shell that is shorter than that, the two being interconnected. Rigidified foam also serving as structural member is arranged between the structural member and the reinforcing shell, through which a trilaminate region, preferably an arch-shaped one, is created. This solution also has the deficiency that the inner member and the outer member are interconnected and fixed to one another decisively through the introduced and rigidified foam, so the mechanical properties of the foam substance may prove to be decisive from the point of view of the absorption of the mechanical forces impacting on it.

The method disclosed by WOO 1/66991 Al also applies foam, notably metal foam, to reinforce a structural arrangement that swells and rigidifies, and fixes the two members in their prescribed position relative to one another when it is introduced into the space between the elements constituting the outer member and the inner member. The advantages and drawbacks of this solu- tion are similar to the state-of-the-art known solutions outlined above.

US 5,255,487 discloses a door reinforcement beam that is part of an arrangement in which two members, namely an outer member and an inner member, are associated. The document considers as default case the design where, for the sake of attaining higher mechanical strength, an outer reinforcement tube, i.e. an outer member, is slipped on an inner member in the range of the expected impact beam, that is meant to provide additional toughness to the tube inside, constituting the actual frame of the vehicle. The solution comprises also the version where the short reinforcing tube section is not slipped on the tube constituting the vehicle frame from the outside, but inserted into it, in the range of attack of the expected impact beam. In order to ensure that the member used as reinforcement placed outside or inside should not slip from its place, the solution proposes to join the two members in one of the customary ways. Typically, each variant aspires to ensure the absorption of bigger forces by increased cross-sections, but in numerous use cases that is not feasible.

Disclosure

Technical Problem The object of the present invention is to develop a load-bearing structural arrangement characterised by substantially bigger strength and flexibility than similar supporting members used so far, but one that is nevertheless relatively light and is not a costly solution. It is important that neither should it be bigger than the beams used so far.

Technical Solution

The task being set has been solved by a load-bearing structural arrangement preferably for a vehicle, comprising a closed outer member defining inner space and inner member arranged in the inner space of outer member, said load-bearing structural arrangement comprises at least one inner member that is a tubular member defining at least one further inner space or a profile member dividing the inner space of the outer member into several parts, the inner member is in linear contact at least at one location with the hosting outer member along at least part of its length, and the inner member and the outer member are attached to each other at least in a pointlike way at intervals along their length.

According to a preferred embodiment of the load-bearing structural arrangement the outer member is an element chosen from a group comprising a hollow section having a circular, oval, a triangular, a polygonal or irregular cross-section.

According to another preferred embodiment of the load-bearing structural arrangement the inner member is an element chosen from a group comprising a hollow section having a circular, oval, a triangular, a polygonal or irregular cross-section.

According to another preferred embodiment the load-bearing structural arrangement is bended in one plane in a least one arc.

According to another preferred embodiment the outer member is a hollows section with square cross-section, the inner member is a hollow section with a circular cross-section, and it is in linear contact with the inner surface of outer member through the inner superficies of inner mem- ber on all of its four sides.

According to another preferred embodiment the outer member is a hollow section with square cross-section, the inner member is a hollow section with triangular cross-section, and inner member is partly in surface and partly in linear contact with the inner surface of outer member on one side of the triangle and its edge opposite to that side.

According to another preferred embodiment the outer member is a hollow section with circular cross-section, the inner member comprises two mutually perpendicular crossed ribs, and the inner member is in four linear contacts with the outer surface of the outer member through the respective ends of the ribs of the inner member. According to another preferred embodiment the outer member and inner member are hollow sections with square cross-section, where inner member is sized so that it is in close surface contact with the inner surface of outer member through its superficies.

According to another preferred embodiment the outer member is a hollow section with racetrack cross-section, the inner member is a hollow section with a cross-section of two triangles turned towards one another with one side, and inner member is in linear contact with the inner surface of outer member through the two opposite edges of the triangles.

According to another preferred embodiment both the outer member and the inner member have cross-sections of an asymmetrically elongated shape.

According to another preferred embodiment the inner member and outer member are attached to one another at intervals along their length by spot welding.

According to another preferred embodiment the inner member and outer member are attached to one another at intervals along their length by riveting.

According to another preferred embodiment the inner member and outer member are attached to one another at intervals along their length by bolted connection.

According to another preferred embodiment the point-like connections between the inner member and outer member are made parallel with the longitudinal axis of the outer member.

According to another preferred embodiment the inner member and outer member are attached to each other in several different planes along their perimeter.

According to another preferred embodiment the interval between two adjacent interconnections between the inner member and the outer member is proportional with the overall cross-sectional dimension of the outer member.

According to another preferred embodiment the interval between two adjacent interconnections of inner member and outer member is the multiple of the overall cross-sectional dimension of the outer member.

According to another preferred embodiment the load-bearing structural arrangement is divided into several sections along its length, where the individual sections comprise inner members of different cross-sections.

Thus I considered it expedient to apply a dual structural arrangement to realise the objective. The idea underlying the invention is that one part - the inner member - is chosen in consideration of the fact that, in the event of bending, material will be compressed along the inside arc of the inclination and extended along the outer one. The part around the symmetry axis is of negli- gible relevance, so it can be omitted. This makes it possible to attain significant weight reduction, without a concurrent decrease in strength. Consequently, a profile with a circular cross- section, that is, a tube is the most appropriate means, but a profile defined by the outer member, of almost any cross-section, is also appropriate as inner member. The essential thing is that it should be possible to slip the inner member into the outer member and there should be as many points of contact as possible between the two members.

The outer member of this structural arrangement also utilises the energies of pressure and traction to enhance strength.

Since the critical part of the bracket and of any support is the arched part, one should focus pri- marily on that. By way of example, I chose as outer member a profile with a square cross- section into which a tube constituting the inner member is fitted.

After several experiments, it has been proved that the load must be divided into sections. This division has been realised by interconnecting, fixing, the outer and the inner member at adequate distances. This has put an end to the uncontrolled combination of movements and defor- mations along long sections. In the event of bending stress, the square section should be sized on its side towards the inclination arc for buckling but here the primary direction of the buckling is given already, towards the inside of the section. It is supported from this direction by the part of the inner member thickened already by the bending, so no buckling is feasible; instead, this part of the outer member must swell under pressure. The energy needed for that, however, in- creases the energy absorbing capacity of the bracket, and increases the energy needed for bending 2.6-2.8 times relative to the original status. Without the divisions at given intervals, but with the dual structure, this value is but 1.5.

The rigidity of the beam can be controlled by the distance between the junction points of the outer and inner members. This value increases with the decrease of the distance and vice versa. Such control is applicable only within certain value ranges. If the distance of the junction points drops below a critical value, the rigidity value will undergo rapid decrease. If the distance between the junction points is raised above the maximum, the bucklings of the outer member will become uncontrollable and the effect described above will cease.

The distance of the junction points depends on the cross-section size and form of the inner and outer members.

The distance between the junction points of a beam may vary according to the load-bearing requirements.

The shape (cross-section) of the inner member may vary within the same beam, also in function of the load-bearing requirements, and in order to attain the lowest possible weight. In this case, such reinforcement should be applied at the connection point of the various inner members as will eliminate the absence of the inner member at the connection point.

Contrary to the name "bracket", the beam can be of almost any form, except that of a twisted spiral form, and the inclinations can only occur along an arch, a radius, of some kind.

The essential components of the arrangement according to the invention are an outer member of any cross-section, an inner member of a cross-section fitting somehow in the outer member and connecting means or e.g. welding used to clench the two mentioned parts.

There may be several inclinations in the beam, but the objective is realised fully by a plane design free of torsion.

Description of Drawings

In what follows, I will describe the invention in more detail with the help of the attached drawing, representing an exemplary embodiment of the proposed load-bearing arrangement. In the drawing,

Figure 1 shows the schematic view of a possible embodiment of the load-bearing structural arrangement according to the invention;

Figure 2 shows the exploded view of a part of the load-bearing structural arrangement according to Figure 1;

Figure 3 shows the parts of the load-bearing structural arrangement according to Figure 1, and

Figures 4a-4f show some preferred embodiments of the inner and outer member constituting the load-bearing structural arrangement according to the invention in schematic sectional view.

Detailed Mode for Invention

Figure 1 shows in lateral view a load-bearing structural arrangement 2 according to the invention, also called "bracket" in this description, attached to a floorboard 1 of a city bus by way of example in the known way. The figure presents in schematic view that load-bearing structural arrangement 2 is rigidly connected to the floorboard 1. The load-bearing structural arrangement 2 is essentially a U-shaped bracket comprising two vertical or partly near-vertical legs 2a and connecting section 2c interconnecting them via arched sections 2b and essentially defining the roof level of a vehicle. Externally, legs 2a, arched sections 2c and connecting section 2c are near-square-shaped, as indicated in the Figure by the small squares drawn into the load-bearing structural arrangement 2. Legs 2a may be completely vertical or their upper section may enclose an angle with the vertical and slant slightly inward. In the embodiment presented here, the cross-section of load-bearing structural arrangement 2 is essentially constant (except for the arcs).

In the schematic representation of Figure 2, one can observe the essential details of the load- bearing structural arrangement according to the invention providing for realising the set task. Accordingly, legs 2a, arched sections 2b and connecting section 2c of the load-bearing structural arrangement 2 consist in the present example of outer member 3 that is square or, more precisely, its cross-section is square and an inner member 5 with circular cross-section extend- ing into its inner space 4 and filling it almost completely. The inner member 5 is arranged within the outer member 3 along its total length, and it is sized so that its external superficies be in contact at least at two points, for three outer members with square cross-section at four points, with the inner surface of the outer member 3. Since the members concerned are not point-like but have a linear dimension, this contact is, mutatis mutandis, not point- but line-like in the presented case.

The outer member 3 and the inner member 5 are attached to each other on all four sides of the square-shaped outer member 3 at given intervals. These junctions 6 are indicated in the figure symbolically, by points. As can be observed, junctions 6 are designed in the longitudinal direction of outer member 3 and hence of inner member 5, parallel with their longitudinal axis, along the linear contact of the outer member 3 and the inner member 5, so that they lie in an identical plane, perpendicular to that of the outer member 3, on all four sides of outer member 3. However, this arrangement is not mandatory, junctions 6 can also be made on individual sides of outer member 3 or along its perimeter, at various points of its perimeter, in various planes that differ from one another.

Junctions 6 may be chosen in function of the material, size and targeted load strength of the outer member 3 and inner member 5 ever. This theorem is equally true for the determination of the distances of junctions 6 from one another. In the embodiment described here, junctions 6 are designed, as can be observed also in the figure, at equal intervals T, but that is not absolutely necessary; junctions 6 can also be designed at different intervals relative to one another depend- ing on the expected loads, targeted load-bearing capacity and strength along the load-bearing structural arrangement 2.

Junctions 6 can be made, for example, by spot welding, bolted connection, riveting or, in an extreme case, special adhesive bonding is also conceivable.

As can be seen also in the Figure, the inner member 5 is not a compact rod-like component, but it can also be a simple or complex hollow section also defining an inner space 7. The possible and, as appropriate, preferred embodiments of the outer member 3 and the inner member 5 will be exemplified later by the aid of Figure 4.

Although in Figure 2 the connecting section 2c can also be interpreted as an element that is separate from the legs 2a, obviously, and particularly in view of the objective, legs 2a and connecting section 2c are cut to size from a single contiguous part in the default case. However, neither is it excluded that, depending on the size and envisaged utilisation of the load-bearing structural arrangement 2, legs 2a and connecting section 2c - together with inner member 5 arranged in them as outer member 3 - be manufactured in several parts, and be connected in the known and appropriate mechanical way into a single load-bearing arrangement.

Figure 3 shows a typical intersection of a portion of the load-bearing structural arrangement 2 presented in Figures 1 and 2. One can recognise there the connecting wall parts of the outer member 3 and the inner member 5 in linear contact with one another, and two rivets applied as junctions 6. The portion shown there is a portion of arched section 2b of the load-bearing struc- tural arrangement 2. Where this load-bearing structural arrangement 2 and this arched section 2b is subject to a force impact marked symbolically with arrow F in Figure 3 - typical in the event of the overturn of a vehicle - it will strive to buckle in the direction of arrow 8 but the wall of inner member 5 in contact with it will hinder that. As no buckling is possible, under the impact of the force (crushing force) marked by an arrow F, the affected part of the outer mem- ber 3, which has thickened anyway relative to its original size as a result of the bending, will strive to swell. That, however, requires such energy as would increase the energy absorbing capacity and the energy needed for bending of load-bearing structural arrangement 2 2.6-2.8 times.

Figures 4a-4f show some potential examples of the design and arrangement relative to each other of outer member 3 and inner member 5. As can be seen, there are always at least two linelike linear contacts between the outer member 3 and the inner member 5, and in several cases (square within the square, triangle within the square) both linear and surface contact is feasible. As will be obvious to a person skilled in the art, the figures shown here are not completely to scale, but are merely meant to promote the better understanding of the solution according to the invention and, furthermore, in some cases (e.g. Figure 4b), the inner space 4 of the outer member 3 is not visible, as it is filled completely by the inner member 5.

Advantageous Effects

As for the technical advantages of the arrangement according to the invention, let's mention easy manufacturing, light weight, small space allowance and high strength. Economic advan- tages include low production cost, competitive market appearance and aesthetic design.

The primary utilisation area is the manufacture of vehicles, particularly of those bus, trolley bus, railway wagon and tram parts starting from the floorboard or the chassis and overarching the roof to ensure the connection between the sub- and the superstructure, i.e. the roof. These pro- vide for the strength of the roof between the end parts and for passenger safety.

The load-bearing structural arrangement according to the invention offers a solution to the problems listed in the introduction, and will make the intercity and tourist buses substantially more secure than buses with other frame structures at a low weight and cost price.

Another utilisation area of the invention is the manufacture of passenger rail cars. The wagons will be lighter and the survival probability of passengers will be enhanced significantly in the event of overturn with derailment.

A similar utilisation option is offered by fixed-rail urban transport, that is, tram superstructures, where the vehicles can be made lighter and hence more economical.

The use of the load-bearing structural arrangement according to the invention may be a solution wherever a steel-structured bended support is needed, that cross-section of which should be as small as possible, at a great strength.

List of used reference signs

1 floorboard

2 load-bearing structural arrangement (=bracket)

2a leg

2b arched section

2c connecting section

3 outer member

4 inner space

5 inner member

6 junction

7 inner space

F arrow

T distance