Chair support

Description

[0001] This utility model relates to the furniture industry, specifically to the design of support bases for chairs, armchairs, stools, and other seating furniture. The claimed technical solution can be used in the manufacture of metal chair supports, primarily for chairs with a central seat attachment point and four spatially spaced legs made of profiled metal tubing.

[0002] The prior art discloses various designs of metal chair frames and furniture supports in which legs, crossbars or other tubular elements are connected to each other by welding, central connecting elements, pressure plates, threaded fasteners or a combination thereof.

[0003] A metal chair frame is known from patent document EP 1259140 A1, "Metal frame for chairs with tubular elements," published on November 27, 2002, applicant Cerantola SpA. The said frame relates to metal chairs made of tubular elements and comprises two inverted U-shaped elements forming the legs, two L-shaped elements forming the support for the seat and backrest, and two rod-shaped cross members connecting the said tubular elements. The connection of the cross members to the U-shaped and L-shaped elements is achieved by contact relief welding along protrusions formed by corresponding recesses and plastic deformation of the cross section of the tubular element. The description of this solution explicitly states that it is aimed at reducing manufacturing time, lowering costs and ensuring the strength of the frame comparable to known designs.

[0004] A disadvantage of this solution, as applied to the claimed chair support, is that the tubular elements are connected by welding and rely on the chair's frame structure with U- and L-shaped elements, rather than a central node in which four independent curved support elements converge in a single central area. The known solution lacks a volumetric central connecting body with lateral receiving sections into which the end portions of the upper sections of the support elements are inserted, and it also lacks an upper pressure plate that ensures the simultaneous pressing of these end portions against the central body. Consequently, this solution does not provide a detachable positioning connection of the four support elements in the central area of ​​the chair support and does not address the issue of improving assembly efficiency by pre-setting the geometric position of each support element within the receiving section of the central body.

[0005] A chair base design is also known from patent document US 2021 / 0007489 A1, "Chair and chair base," published on January 14, 2021. This solution discloses a chair base comprising a vertically positioned connecting pipe, four support legs arranged in four directions around said connecting pipe, and two C-shaped rotating rods. The description indicates that the four support legs are arranged in the front, rear, left, and right directions, respectively, and jointly support the connecting pipe; some of the legs are fixed, while others are rotatable, allowing the base to be folded.

[0006] The disadvantage of this solution is that it is primarily designed to create a folding chair base and uses hinge elements, sliding bushings, C-shaped pivot rods, and rods. It lacks a rigid cross-shaped connection between the four upper sections of the support elements, in which the end sections of the profile tubes fit into the side receiving sections of the volumetric central body and are secured from above by a pressure plate. This known base has a different kinematic design and does not disclose the design of a detachable clamping connection between the four curved support elements, which ensures their precise mutual positioning in the central zone.

[0007] A furniture base with a central collector is also known from patent document US 8303041 B2, "Furniture base with central collector." In this solution, the furniture base may comprise four legs and a central collector. The description discloses that each leg has an upper and lower portion, and the central collector contains several compartments that accommodate portions of the corresponding legs. After inserting the legs into the collector, they can be rotated relative to the collector and then secured, for example by welding, forming a spatial furniture base.

[0008] This solution is similar in its general concept of using a central element housing portions of several legs. However, it does not disclose a pressure plate located above the ends of the four upper sections of the support elements and connected to the central body via threaded fasteners, allowing for simultaneous clamping of these portions. Furthermore, in the prior art solution, securing the legs after installation in the manifold requires welding or a similar fastening method, whereas the claimed chair support provides a detachable or primarily detachable connection, in which retention is achieved by the combined action of the lateral receiving portions of the central body and the upper pressure plate. Consequently, the prior art solution does not provide the same maintainability, assembly manufacturability, or the ability to precisely position the ends of the profile tubes without a final weld.

[0009] A table support connection assembly is known from Russian Federation Patent RU 2302563 C1, "Table Support Connection Assembly." This solution relates to furniture manufacturing and is designed to connect table legs to frame components. The assembly comprises a vertical support, horizontal crossbars with internal threaded elements, and an additional element shaped like a cup, the bottom of which is fastened to the support, and the side walls to the crossbars. The description states that this design is intended to increase the strength, manufacturability, and versatility of the assembly.

[0010] Patent RU 2302563 C1 also discloses that known connections for tubular furniture elements can quickly become loose, lack strength, and are difficult to manufacture, particularly due to the use of gussets, slots, or complex stamped elements. The solution in RU 2302563 C1 itself proposes using a cup with side holes to which horizontal crossbars are attached. The holes can be horizontally elongated to improve versatility and facilitate adjustment during assembly.

[0011] A disadvantage of RU 2302563 C1, as applied to the claimed chair support, is that it refers to the connection between the vertical table support and horizontal crossbars and presupposes the presence of a central vertical post. However, the claimed design is a chair support without a central vertical leg, in which four curved support elements themselves form a spatial load-bearing system. Furthermore, in RU 2302563 C1, the crossbars are attached to the side walls of the cup using bolts and internal threaded elements, rather than being inserted with their end sections into the side receiving sections of the central body and then simultaneously pressed from above by a common pressure plate. Therefore, this solution does not disclose the claimed method for connecting the four supporting elements of the chair in the central zone.

[0012] The closest analogue to the claimed utility model is patent document US 2815801 A, "Leg clamp for chairs and the like," published on December 10, 1957. This solution discloses a seat with two pairs of tubular legs, wherein the upper horizontal sections of the pairs of legs are arranged in an intersecting manner and are clamped between an upper clamping plate and a lower cup-shaped clamping plate. The description indicates that the horizontal sections of the leg pairs can be welded and clamped between the upper disc-shaped clamping plate and the lower cup-shaped clamping plate, and the fasteners are tightened to securely fix the tubular sections relative to the bottom of the seat.

[0013] This solution was chosen as a prototype because, like the claimed utility model, it relates to fastening the tubular leg elements of a chair in the area beneath the seat and uses clamping plates and threaded fasteners to secure the horizontal leg sections. The prototype also discloses that the tubular horizontal leg sections can pass through cutouts in the bottom plate, and the bolts, when tightened, press them between the plates, ensuring fastening to the underside of the seat.

[0014] A drawback of the prototype is that the tubular leg elements are primarily clamped between the upper and lower plates. It does not disclose a volumetric central connecting body with lateral receiving sections into which the end sections of the four independent upper sections of the support elements are inserted. The prototype utilizes two pairs of legs connected by upper horizontal tubular sections, which can be welded or additionally clamped together at the intersection. This solution does not allow for the individual insertion of each of the four upper sections of the profile tubes into the corresponding lateral receiving section of the central body and does not ensure the displacement of each end section is limited by the walls of the volumetric body in combination with the upper clamping plate.

[0015] The technical result of the claimed utility model consists in increasing the rigidity, reliability and manufacturability of the connection of the supporting elements of the chair in the central zone.

[0016] The technical result is achieved due to the fact that the chair support contains four curved support elements made from a metal profile pipe, each of which contains a horizontal upper section, a curved transition section and a lower section forming a leg, the horizontal upper sections of the four support elements are arranged crosswise and connected in the central zone by means of a central connecting unit, including a central connecting body and an upper clamping element, connected to each other by threaded fasteners, wherein in the central connecting body and / or in the upper clamping element, lateral receiving sections are made for accommodating the end parts of the horizontal upper sections of the support elements, wherein the central connecting body and the upper clamping element are designed with the possibility of mutually tightening and fixing the end parts of the horizontal upper sections of the support elements in the central zone.

[0017] Preferably, the central connecting body and the upper pressing member have a geometrically similar shape.

[0018] Preferably, the central connecting body and the upper clamping element are arranged in a mirror image relative to the plane of placement of the horizontal upper sections of the support elements.

[0019] Preferably, the central connecting body and the upper pressing element are designed in the form of two mating body elements, each of which contains lateral receiving sections for accommodating at least a portion of the end portions of the horizontal upper sections of the support elements.

[0020] Preferably, part of the end portions of the horizontal upper sections of the support elements are located in the side receiving sections of the central connecting body, and another part of the end portions of the horizontal upper sections of the support elements are located in the side receiving sections of the upper pressing element.

[0021] Preferably, the end portions of two oppositely located support elements are placed in the side receiving sections of the central connecting body, and the end portions of two other oppositely located support elements are placed in the side receiving sections of the upper pressing element.

[0022] Preferably, the side receiving sections are configured to cover the end portions of the horizontal upper sections of the support elements on at least two sides.

[0023] Preferably, when the central connecting body and the upper clamping element are mutually tightened, the end parts of the horizontal upper sections of the support elements are clamped between the said elements with limitation of their displacement in the vertical and horizontal directions.

[0024] Preferably, the central connecting body and the upper clamping element are provided with aligned fastening holes through which threaded fastening elements are passed.

[0025] Preferably, the central connecting body and the upper pressing member form a closed or partially closed volumetric connecting block after being pulled together.

[0026] The chair's design features four curved support elements made of metal tubing. Each element comprises a horizontal upper section, a curved transition section, and a lower section forming the leg. This creates a spatial load-bearing system in which the seat load is transferred not through separate flat or locally fixed components, but through extended tubular elements with a developed modulus of resistance. Constructing the support elements from metal tubing ensures high resistance to bending, torsion, and localized buckling while maintaining a relatively low weight. The horizontal upper section serves as the load entry point into the central zone, the curved transition section ensures a smooth change in load direction without creating sharp stress concentrators, and the lower section, forming the leg, supports vertical and lateral operational loads.Due to this consistent geometry, each support element functions as a single spatial beam, which contributes to increased rigidity, reliability, and the technological effectiveness of connecting the chair's support elements in the central zone, since the central node interacts with pre-oriented horizontal sections of pipes that have a stable cross-section and geometry that is convenient for fixation.

[0027] The cross-shaped arrangement of the horizontal upper sections of the four support elements and their connection in the central zone via a central connecting unit, comprising a central connecting body and an upper clamping element, connected by threaded fasteners, creates a symmetrical center of force for the chair support. This cross-shaped arrangement ensures even distribution of seat forces in four directions and reduces the likelihood of distortion, as the load is supported not by a single fastening line, but by a system of mutually oriented elements. The central connecting body serves as the lower or main support portion of the unit, and the upper clamping element functions as a counter-clamping element, which, when tightened, creates a normal clamping force and secures the tubular elements in position.The use of threaded fasteners allows for adjustable clamping force, assembly without welding or with minimal welding, and ensures maintainability and repeatability of the connection. This design directly increases the rigidity, reliability, and manufacturability of the connection between the chair's supporting elements in the central zone, as the connection takes on the character of a detachable, power-clamping unit with controlled clamping force.

[0028] The inclusion of lateral receiving sections in the central connecting body and / or in the upper clamping element for accommodating the end sections of the horizontal upper sections of the support elements ensures not only the clamping of the pipes but also their geometric positioning relative to the central zone. The lateral receiving sections define the insertion direction of each profile pipe, limit its transverse displacement, and reduce the dependence of assembly accuracy on the skill of the assembler. When the end sections of the pipes are placed in such sections, the forces from the support elements are transferred to the body parts through an increased contact area rather than through individual attachment points, reducing contact stress and the risk of deformation of the profile pipe walls.The ability to tighten the central connecting body and the upper clamping element creates a stable clamping connection, preventing the ends of the horizontal upper sections from falling out and also preventing rotation, shear, and loosening during operation. This increases the rigidity, reliability, and adaptability of the connection between the chair's supporting elements in the central zone, as the connecting unit simultaneously functions as a positioning, clamping, and load-bearing device.

[0029] The geometrically similar shape of the central connecting body and the upper clamping element facilitates a consistent distribution of forces during their mutual compression. This geometric similarity of these elements ensures uniform contact in the mating zone, eliminates localized distortions when tightening threaded fasteners, and creates a structurally predictable load transfer pattern from one housing element to another. With this arrangement, the upper clamping element is not a random overlay but a functionally coordinated counterpart to the central connecting body, reducing the likelihood of uneven clamping of individual pipes and increasing the stability of all four support elements. Furthermore, geometrically similar parts are easier to manufacture, as they can be produced using similar operations such as forming, bending, stamping, casting, machining, or cutting.This feature is aimed at increasing the rigidity, reliability and manufacturability of the connection of the supporting elements of the chair in the central zone, since it ensures the structural consistency of the clamping elements and increases the reproducibility of the assembly.

[0030] The mirror-image arrangement of the central connecting body and the upper clamping element relative to the plane of the horizontal upper sections of the support elements creates a balanced clamping unit, in which the clamping forces are applied to the tubular elements symmetrically relative to their working plane. This arrangement reduces the likelihood of bending or extrusion of the end sections of the profile tubes from their seating zones when tightening the fasteners. With this mirror-image arrangement, the body elements act as two coordinated halves of a spatial lock, with the horizontal sections of the support elements positioned between them, increasing the resistance of the connection to opening, rotation, and lateral displacement. The mirror-image arrangement also facilitates assembly, as the orientation of the parts becomes obvious, and the relative positions of the upper and lower sections of the assembly are determined by the geometry itself.Consequently, this feature ensures increased rigidity, reliability and manufacturability of the connection of the supporting elements of the chair in the central zone, as it facilitates symmetrical clamping of the pipes and reduces installation errors.

[0031] The central connecting body and upper clamping element are designed as two mating body elements, each containing lateral receiving sections for accommodating at least a portion of the end portions of the horizontal upper sections of the support elements. This allows for the formation of a three-dimensional detachable assembly operating on the principle of a spatial cage. Unlike a joint in which the pipes are simply applied to a flat plate, the mating body elements partially enclose and guide the end sections of the pipes, ensuring their fixation at specified angular positions. The presence of receiving sections in both body elements increases the area of ​​interaction with the pipes and allows for load distribution between the upper and lower sections of the assembly.Assembly can be accomplished by inserting a portion of the pipes into the receiving sections of one element, then installing the mating element and tightening them with fasteners, simplifying installation and reducing the need for welding. This feature improves the rigidity, reliability, and ease of use of the chair's support elements in the central area, as it combines the functions of the guide rail, load-bearing frame, and clamping fixture.

[0032] Placing some of the end sections of the horizontal upper sections of the support elements in the lateral receiving sections of the central connecting body, and the other end sections of the horizontal upper sections in the lateral receiving sections of the upper clamping element, allows for the efficient height distribution of intersecting tubular elements and avoids geometric conflicts in the central zone. With this design, each group of pipes receives its own landing zones, and the body elements, when pulled together, mutually secure pipes in different directions, forming a spatially closed system. This reduces the need for complex cutouts in the pipes or excessive weakening of their walls, since the intersection is ensured by the design of the connecting unit.This arrangement also facilitates assembly: the ends of some support elements can be placed in one frame element, while the ends of others can be placed in the opposite frame element, after which the entire assembly is fastened together. This feature increases the rigidity, reliability, and ease of assembly of the chair's support elements in the central area, as it streamlines the relative positioning of the pipes and prevents uncontrolled overlapping of elements at the intersection.

[0033] The placement of the end sections of two oppositely positioned support elements in the lateral receiving sections of the central connecting body, and the end sections of two other oppositely positioned support elements in the lateral receiving sections of the upper clamping element, ensures force symmetry of the connection. With this arrangement, each pair of opposite support elements is perceived by the corresponding body element as a single force transmission line, while the other pair is fixed by a counter element in a perpendicular or nearly perpendicular direction. This reduces stress concentration in one area, ensures uniform distribution of bending and torsional moments, and increases support stability under loads applied to the seat in various directions.Furthermore, separating the two pairs of opposing tubes between the two body elements simplifies assembly, as each pair can be installed in its respective receiving areas without interfering with each other. This solution is aimed at increasing the rigidity, reliability, and ease of assembly of the chair's support elements in the central zone, as it ensures a symmetrical load-bearing structure and predictable positioning of all four support elements.

[0034] The design of lateral receiving sections capable of enclosing the ends of the horizontal upper sections of the support elements on at least two sides ensures stable support of the profile pipes not only due to frictional force from the clamping force but also by geometrically limiting their movement. Enclosing on both sides prevents lateral displacement of the pipe, its rotation around its longitudinal axis, and changes in its angular position relative to the central node. This is especially important for profile pipes, as their flat walls allow for a stable mating with the mating surfaces of the receiving sections, and contact on multiple sides increases resistance to loosening under cyclic loads. This type of enclosing also reduces the risk of localized pipe wall collapse, as the force is distributed across multiple contact surfaces.As a result, this feature ensures increased rigidity, reliability and manufacturability of the connection of the supporting elements of the chair in the central zone, since the receiving section performs the function of a guide and retaining support for the end part of the pipe.

[0035] Clamping the ends of the horizontal upper sections of the support elements between the central connecting body and the upper pressure element while pulling them together, limiting vertical and horizontal displacement, ensures spatial fixation of the pipes in the central zone. Limiting vertical displacement prevents the pipes from leaving the support plane and reduces the likelihood of the connection opening under seat loads, while limiting horizontal displacement prevents the support elements from spreading and changes in the geometry of the chair base. At the same time, the clamping between the two body elements creates a pre-stressed state of the joint, increasing resistance to micro-movements and vibration-induced weakening. By combining force clamping and geometric constraint, the connection becomes more resistant to repeated operational loads arising from user seating, chair movement, tilting, and lateral impacts.This feature directly increases the rigidity, reliability, and manufacturability of the connection of the chair's supporting elements in the central zone, as it creates a three-dimensional fixation of the pipes without the need for complex welded assembly.

[0036] Providing the central connecting body and upper clamping element with aligned mounting holes through which threaded fasteners are passed ensures precise relative alignment of the connected body parts and the creation of a controlled clamping force. The aligned holes serve not only as a fastener passage but also as an assembly reference, since when fasteners are installed, the body and clamping element occupy a predetermined relative position. Threaded fasteners ensure repeatable tightening force, enable assembly control, allow disassembly of the connection, and allow for the replacement of individual components during repair or modernization. Furthermore, the use of threaded fasteners improves the manufacturability of mass production, as it eliminates the need for mandatory welds in the central zone, which could cause warping, thermal weakening of the metal, and geometric variation.This feature helps to increase the rigidity, reliability and manufacturability of the connection of the supporting elements of the chair in the central zone, since it provides controlled force closure of the central unit.

[0037] The formation of a closed or partially closed volumetric connecting block after tightening by the central connecting body and the upper clamping element transforms the central zone from a set of individual contacting parts into a single spatial load-bearing structure. A closed or partially closed volumetric block offers increased resistance to bending and torsion compared to flat pads or point fasteners, since its walls and mating surfaces work together, supporting loads in different directions. This connection reduces the risk of clamping zone opening, localized tube displacement, and gradual loosening during cyclic operation of the chair. Furthermore, the volumetric block protects the ends of the horizontal upper sections from accidental external impact, improves the accuracy of the design, and allows for standardization of the central unit as a separate assembly unit.This feature ensures increased rigidity, reliability and manufacturability of the connection of the supporting elements of the chair in the central zone, since the central connecting unit acquires the properties of a spatial body that perceives and redistributes operational loads between all supporting elements.

[0038] Taken together, these features form a technical solution in which the central support zone of the chair is designed not as a simple point of convergence of individual legs, but as a volumetric clamping and positioning unit, ensuring the precise relative positioning of four curved tubular support elements. The central connecting body and the upper clamping element, interacting through threaded fasteners and lateral receiving sections, provide forceful tightening, geometric alignment, limited displacement, and uniform load distribution. This results in increased rigidity, reliability, and manufacturability of the connection of the chair's supporting elements in the central zone, as the design combines spatial rigidity, resistance to operational loosening, ease of assembly, maintainability, and the ability to manufacture the connecting unit as a repeatable technological element.

[0039] To explain the essence of the device, the following figures are presented:

[0040] Fig. 1 - External appearance of the claimed device;

[0041] Fig. 2 - External appearance of the central connecting unit.

[0042] The claimed chair support can be implemented as a metal spatial base designed for installation under the chair seat and supporting operational loads from a seated user, the weight of the seat, as well as lateral and torsional forces arising from the chair's movement, sitting, standing, and leaning. The support comprises four curved support elements converging in a central area and connected to each other by a central connecting unit. The central connecting unit is designed such that it not only tightens the support elements with threaded fasteners but also determines their relative spatial position by locating the end portions of said support elements in the receiving sections of the connecting elements.

[0043] Each support element is preferably made of a metal profile tube of rectangular, square, oval, rounded rectangular, or similar cross-section. Support elements are preferably made of a profile tube with rounded corners, as this tube provides sufficient bending rigidity with a relatively low weight, is easy to bend, and has technologically suitable flat or slightly convex surfaces for making holes and mating with the connecting unit. Steel, stainless steel, aluminum alloy, or other structural metal material suitable for the manufacture of furniture supports can be used as the material. When using a steel profile tube, the support elements can have a protective and decorative coating, including powder polymer coating, galvanic coating, paint and varnish coating, oxide coating, or a combination of surface treatments.

[0044] Each support element is elongated and comprises a horizontal upper section designed to be positioned under the chair seat, a curved transition section, and a lower section forming the leg. The horizontal upper section serves both as a load-bearing element, transmitting the load from the seat to the central connecting unit, and as a mounting section, through which the support element can be further connected to the seat or to an intermediate seat mounting platform. The curved transition section provides a smooth transition from the horizontal upper section to the lower section forming the leg, thereby eliminating the need for a welded connection between the upper section and the leg. The lower section is positioned primarily vertically or at a slight angle relative to the vertical and is designed to rest on the floor via an end piece, plug, heel pad, plastic insert, rubber support, or other supporting element.

[0045] In the preferred embodiment, each support element is manufactured as a single piece of profile tubing by bending. This design increases the strength of the support element, as there is no weld seam in the most heavily loaded transition zone from the horizontal section to the leg. The bending radius of the transition section is selected to ensure the maintenance of the load-bearing cross-section of the tubing without critical wall collapse, rupture of the outer wall, or the formation of excessive folds on the inner side of the bend. Depending on the dimensions of the chair and the cross-section of the tubing, the bending radius along the centerline of the tubing can range from 30 to 180 mm, preferably from 45 to 120 mm. When using profile tubing with a greater cross-sectional height, the bending radius is selected to be larger to ensure dimensional stability and repeatable geometry of the support elements.

[0046] The cross-section of the profile tube can range from 15×15 mm to 50×50 mm for a square design, or from 15×20 mm to 40×70 mm for a rectangular design. For household and office chairs, it is preferable to use a tube with dimensions from 20×20 mm to 30×40 mm. The tube wall thickness can range from 0.8 to 3.5 mm, preferably from 1.2 to 2.5 mm. A smaller wall thickness reduces the weight of the product and makes bending easier, but reduces resistance to localized crushing in the clamping zone. A greater wall thickness increases the rigidity and durability of the structure, but increases the weight and bending complexity. The length of the horizontal upper section of each support element from the central connecting node to the bending zone can range from 120 to 450 mm, preferably from 180 to 350 mm. The height of the lower section that forms the leg can be from 250 to 550 mm, preferably from 350 to 470 mm for a regular chair.The ranges given may vary depending on the intended use of the product, seat height and required load-bearing capacity.

[0047] The horizontal upper sections of the four support elements are arranged in a cross-shaped pattern, with two opposing support elements located along one conventional longitudinal axis, and the other two opposing support elements along another conventional transverse axis. The angle between these axes is preferably between 70 and 110°, preferably between 85 and 95°, and most preferably around 90°. This cross-shaped arrangement ensures uniform load distribution across the four legs and the formation of a stable support contour. In certain embodiments, the axes of the pairs of support elements may intersect at an angle other than right angles, for example when designing a chair with an asymmetrical seat, an offset backrest, decorative base geometry, or a special purpose.

[0048] The central connecting node is located at the intersection of the horizontal upper sections of the support elements. It may be implemented as two connecting elements tied together, namely a first connecting element and a second connecting element. In one embodiment, the first connecting element serves as the central connecting body, and the second connecting element serves as the upper clamping element or clamping plate. In another embodiment, more preferred for strengthening the connection, the first and second connecting elements are implemented as housing elements of the same or geometrically similar shape, installed opposite or mirror image to each other. In this embodiment, each of the connecting elements contains its own lateral receiving sections designed to accommodate the end portions of the corresponding horizontal upper sections of the support elements.

[0049] The first connecting element may be located below the plane of the horizontal upper sections, and the second connecting element may be located above. In this case, some of the end portions of the horizontal upper sections of the support elements may be inserted into the lateral receiving portions of the first connecting element, and the other part of the end portions of the horizontal upper sections may be inserted into the lateral receiving portions of the second connecting element. For example, the end portions of two opposite support elements located along the longitudinal axis may be placed in the receiving portions of the lower connecting element, and the end portions of two other opposite support elements located along the transverse axis may be placed in the receiving portions of the upper connecting element.When the connecting elements are pulled together, a single volumetric central unit is formed, in which each pair of supporting elements is held not only by the frictional force from tightening the fasteners, but also by the geometry of the corresponding receiving section.

[0050] In another embodiment, all four end sections of the horizontal upper sections can be inserted into the lateral receiving sections of a single central connecting body, and the second connecting element can be designed as an upper pressure plate overlapping the aforementioned end sections from above. This embodiment is simpler to manufacture, since the receiving sections are formed in only one housing element. However, the embodiment with two mirror-image housing elements improves the symmetry of the assembly, standardizes the components, and distributes the holding functions between the upper and lower elements.

[0051] The first and second connecting elements may have a square, rectangular, diamond-shaped, cross-shaped, polygonal, round, or a combination of these shapes in plan. A square or near-square shape is most preferable, since it aligns with the cross-shaped arrangement of the four support elements and allows fasteners to be placed in corner areas free from pipe passages. The overall dimensions of the connecting unit in plan may be from 50×50 mm to 180×180 mm, preferably from 70×70 mm to 130×130 mm. The height of each body connecting element may be from 8 to 45 mm, preferably from 12 to 30 mm. The total height of the central connecting unit after tightening the two connecting elements may be from 18 to 80 mm, preferably from 25 to 55 mm.

[0052] Connecting elements can be made from sheet metal, rolled section metal, stamped parts, cast parts, milled blanks, welded blanks, or a combination thereof. When manufactured from sheet metal, the side receiving sections can be formed by bending the edge sections, welding the side walls, installing overhead clamps, forming U-shaped pockets, or welding sections of profile pipe. When manufactured from solid or cast blanks, the receiving sections can be machined into grooves, channels, nests, or recesses. When manufacturing a welded connecting element, the side walls and support pads can be made from separate plates welded together to form a spatial housing.

[0053] The lateral receiving sections of the connecting elements can be designed as open grooves, sockets, pockets, channels, or enclosing guides. Each receiving section preferably has a shape that matches the outer profile of the end portion of the horizontal upper section of the supporting element. If the supporting element is made of a rectangular profile pipe, the receiving section may be U-shaped or partially closed with a lower support wall and two side walls. If the receiving section is located in the upper connecting element, it can be designed inversely, that is, with an upper support wall and side walls enclosing the pipe from above and on the sides. When the upper and lower connecting elements are tightened, these receiving sections jointly limit vertical and transverse displacement of the pipe, and prevent rotation around the longitudinal axis.

[0054] The width of the receiving section can correspond to the width of the profile tube with a technological gap of 0.1 to 3.0 mm, preferably 0.2 to 1.5 mm. The height of the receiving section can correspond to the height of the profile tube or be less than it if the final clamping is ensured by a second connecting element. The insertion depth of the end of the support element into the receiving section can range from 15 to 100 mm, preferably 25 to 70 mm. A depth of less than 15 mm may reduce the resistance of the connection to bending and torsional loads, and a depth of more than 100 mm increases the size and weight of the central unit without significantly improving the operational efficiency of a conventional chair. Preferably, the length of the contact zone between the end of the profile tube and the receiving section exceeds the height of the pipe cross-section by at least 1.0 to 2.5 times, which helps reduce local stress and improve the positional stability of the support element.

[0055] The receiving sections may be open at the end to allow the insertion of the end sections of the support elements toward the center of the assembly. Alternatively, the receiving sections may have side cutouts or windows through which the end sections of the pipes are inserted during assembly, followed by tightening of the connecting elements. The ends of the end sections of the support elements may be straight, oblique, stepped, with cutouts, chamfers, or rounded. In a specific embodiment, the ends may rest against internal stops of the connecting element, which further defines the insertion depth and prevents the support element from shifting toward the center. Internal housing walls, projections, thrust plates, crossbars, flanges, welded stops, or sections of threaded bushings may serve as stops.

[0056] The first and second connecting elements are connected using threaded fasteners. These fasteners can include screws, bolts, studs and nuts, Allen screws, countersunk, semi-countersunk, cylindrical, semi-circular, or flat-head screws. The number of fasteners can range from two to eight, with four being preferred. The most efficient arrangement is for four fasteners to be positioned in the corners of the central connecting node, as this placement prevents the fasteners from intersecting the entry areas of the profile pipes and creates a uniform clamping force across the entire node. The thread diameter of the fasteners can range from M4 to M12, with M5 to M8 being preferred for home and office chairs. For increased loads, M8-M10 fasteners or additional fasteners can be used.

[0057] The first connecting element and the second connecting element may each have aligned fastening holes. In one embodiment, one of the holes is through, and the other is threaded. In another embodiment, both holes are through, and tightening is ensured by a nut located on the opposite side of the connecting unit. In yet another embodiment, one of the connecting elements is equipped with cage nuts, threaded bushings, weld nuts, pressed-in threaded elements, or threaded plates. To prevent loosening, spring washers, serrated washers, lock washers, self-locking nuts, anaerobic thread locking compound, deformable thread inserts, or other means of securing the threaded connection may be used.

[0058] When assembling the chair support, four support elements are first machined to a predetermined shape. Mounting holes for attaching to the seat can be made in the upper horizontal sections. These holes can be round, oval, oblong, or a combination of these. The diameter of round holes can range from 4 to 12 mm, preferably from 5 to 8 mm. Oblong holes can be 4 to 12 mm wide and 8 to 30 mm long. The oblong shape of the holes compensates for manufacturing tolerances in the seat, mounting plate, or support itself, and also facilitates alignment of the mounting holes during assembly. The holes are preferably located in the horizontal upper sections at a distance of 40 to 250 mm from the central connecting node to ensure that the load from the seat is transferred not only through the central area but also through the extended sections of the support elements.

[0059] Next, the end sections of the horizontal upper sections are inserted into the lateral receiving sections of the first and / or second connecting element. For the version with two mirror-image housing elements, two opposite pipes can be pre-installed in the receiving sections of the lower connecting element, after which the other two opposite pipes are installed in the receiving sections of the upper connecting element. The connecting elements are then aligned so that the fastening holes are coaxial, and the end sections of all four support elements are located in the central zone in a cross-shaped pattern. Threaded fasteners are then installed through the holes and tightened. As a result, the first and second connecting elements are pulled together, clamping the ends of the profile pipes and forming a spatial locking unit.

[0060] In the version where the upper connecting element is designed as a pressure plate without its own deep receiving sections, assembly is performed by inserting all four end sections of the support elements into the receiving sections of the lower central connecting body. After they are positioned, the pressure plate is placed on top, the mounting holes are aligned, and the screws or bolts are tightened. The pressure plate prevents the profile pipes from exiting the receiving sections upward, and the side walls of the body prevent the pipes from shifting horizontally. This connection is detachable and allows for the replacement of an individual support element without destroying the entire support.

[0061] In a specific embodiment, the central connecting unit may be additionally equipped with a central insert, spacer element, spacer sleeve, or internal stop located between the first and second connecting elements. Such a component can establish a minimum gap between the connecting elements, limit excessive compression of the profile pipes during fastener tightening, and improve assembly repeatability. Spacers can be implemented as bushings around the fasteners, a central projection, a welded washer, a stiffener, or a thrust plate. The height of the spacers can range from 2 to 30 mm, depending on the height of the pipe cross-section and the configuration of the receiving sections.

[0062] In another design, the connecting unit may be equipped with shear-resistant elements that interact with the ends of the supporting elements. These elements may include projections, pins, bent tongues, ribs, notches, localized indentations, thrust beads, or roughened contact surfaces. They may fit into holes, process recesses, or depressions in the profile pipe, or simply increase shear resistance through localized contact. This design is appropriate for applications with increased requirements for the connection's resistance to cyclic loads and loosening.

[0063] Alternatively, the ends of the horizontal upper sections of the support elements may have additional cutouts, bevels, longitudinal slots, localized flattening, or molded sections to ensure a tighter fit with the receiving sections of the central unit. For example, the end of the profile pipe may be partially crimped or calibrated to ensure a stable insertion into the receiving section. Alternatively, the end of the pipe may be chamfered at an angle of 15 to 60° to facilitate installation. In yet another embodiment, through-holes may be drilled in the pipe for additional fixing pins or screws; however, to maintain maintainability, it is preferable to use a clamping connection without permanently deforming the supporting elements.

[0064] The central connecting unit can be designed as fully detachable, partially detachable, or a combination of the two. In the fully detachable version, all four support elements are held in place solely by geometric placement in the receiving sections and tightening the connecting elements with threaded fasteners. This design is convenient for transportation, repair, component replacement, and coating changes. In the partially detachable version, some of the support elements can be additionally tack-welded, soldered, riveted, or adhesively bonded to one of the connecting elements, while the remaining support elements are detachably held. In the combination version, the threaded connection serves as the primary force connection, and tack welds, thread locking, or point stops are used solely to prevent displacement during assembly and transportation.

[0065] The support can have various spatial geometry options. In the preferred embodiment, the four legs are arranged symmetrically relative to the central connecting unit, and the lower sections of the legs form a rectangular or square support contour in plan. The support contour size in width and depth can range from 300 to 700 mm, preferably from 400 to 600 mm. For a chair with a wide seating area, the support contour can be increased. For a compact chair or stool, the support contour can be reduced. The lower sections of the legs can be positioned strictly vertically or have an outward slope of 1 to 15° relative to the vertical. A slight outward slope increases the chair's resistance to tipping, but an excessive slope increases the occupied space and may impair ergonomics.

[0066] The lower ends of the legs can be open or closed, equipped with foot pads or adjustable feet. The foot pads can be made of plastic, rubber, metal, or a combination of these. When using adjustable feet, threaded bushings or nuts can be installed in the lower ends of the profile tubes, into which the adjustable foot pads are screwed. This design compensates for uneven floors and ensures the chair remains stable without wobbling.

[0067] The surface of the connecting elements can be machined, cleaned, sanded, painted, galvanized, chromed, nickel-plated, or powder-coated. If the connecting unit is located under the seat and is not visible during normal use, its surface may be machined without decorative polishing. If the connecting unit is visible, its outer surfaces may be decoratively finished, with rounded edges, chamfers, or protective covers. The sheet metal thickness for the body elements can range from 1.5 to 8 mm, preferably from 2 to 5 mm. When manufacturing from thinner sheet metal, it is advisable to use flanging and stiffening ribs to increase bending resistance. When manufacturing from thicker material, the receiving sections can be machined or welded from individual walls.

[0068] In one preferred embodiment, the first and second connecting elements are identical in shape and comprise metal housings, each containing two oppositely positioned lateral receiving areas for profile pipes. These housings are installed mirror image to each other, rotated 90° in plan, so that the receiving areas of one element are oriented to accommodate the first pair of opposite support elements, while the receiving areas of the second element are oriented to accommodate the second pair of opposite support elements. When these elements are tightened together with fasteners, a compact central block is formed, in which four pipes are arranged crosswise, but without the need for complex welding in the central area.The same shape of the connecting elements simplifies production, since the same tooling, one type of workpiece, and a single technological process can be used to produce the upper and lower parts of the unit.

[0069] In another preferred embodiment, the first connecting element is designed as a three-dimensional central body with four lateral receiving sections arranged in a cross, while the second connecting element is designed as a flat upper pressure plate. The receiving sections of the central body may be formed by four lateral windows or grooves into which the end sections of the pipes are inserted. The pressure plate may be square and have four fastener holes. This embodiment is characterized by the simplicity of manufacturing the upper element and ease of assembly, since all supporting elements are first positioned within a single body and then simultaneously clamped from above.

[0070] In another embodiment, the central connecting unit can be designed with an intermediate plate located between the two levels of support elements. This intermediate plate can separate pairs of pipes, prevent them from rubbing against each other, set the vertical position of each pair, and increase the rigidity of the unit. The thickness of the intermediate plate can range from 1 to 6 mm. It can be welded to one of the connecting elements or installed freely during assembly.

[0071] An option is also possible in which the first pair of opposing support elements is positioned slightly higher than the second pair of opposing support elements. The difference in height can range from 2 to 40 mm, preferably from 5 to 25 mm. This design is convenient when profile pipes intersect in the central area, as it avoids mutual interference between the pipe cross-sections and ensures a tight fit of each pair in the corresponding receiving element. In this case, the upper surface of the central unit can remain flat or nearly flat for attaching the seat or mounting platform.

[0072] To increase connection rigidity, the receiving sections can be designed so that the ends of the pipes fit into them with minimal installation clearance. After tightening the fasteners, the pipes are pressed against the supporting walls of the receiving sections, while the side walls prevent them from rotating. This design allows for load redistribution: part of the load is supported by the threaded fasteners for tension and shear, part by the contact surfaces of the receiving sections for compression, and part by frictional forces between the pipes and the connecting elements. This allows the central unit to function as a spatial power unit rather than a simple flat screw connection.

[0073] The claimed design allows for varying the number of support elements in specific implementations, such as three, five, or six support elements. However, the preferred and illustrated variant is a four-support structure, which ensures the chair's stability while being easy to manufacture. While maintaining the general connection principle, the receiving sections of the central assembly can be arranged not only crosswise but also radially, with a different angular pitch corresponding to the number of support elements.

[0074] During operation, the vertical load from the seat is transferred to the horizontal upper sections of the support elements and then through the curved transition sections to the lower sections of the legs. Lateral loads and torques are supported by the central connecting unit due to the interlocking arrangement of the pipe ends in the receiving sections and the tightening of the connecting elements with fasteners. When attempting to rotate or shift one of the support elements, its end rests against the side walls of the receiving section, reducing the load on the threaded fasteners and preventing loosening of the connection. Moreover, the upper and lower connecting elements, especially in the mirror-image design, form a mutually closed structure, ensuring the spatial rigidity of the central zone.

[0075] Thus, the proposed chair support can be manufactured using readily available manufacturing processes: cutting, bending, drilling, fabricating connecting elements from sheet or profile metal, welding or bending body parts, installing fasteners, and applying a protective coating. The ability to create the first and second connecting elements of the same shape and their mirror-image arrangement further enhances manufacturability by reducing the number of parts and simplifying assembly. Placing some of the supporting elements in one connecting element and the other in a second connecting element creates a compact central unit with a predetermined mutual tube position, high rigidity, secure fixation, and the ability to disassemble for repairs or transportation.

Claims

1. A chair support comprising four curved support elements made from a metal profile pipe, each of which comprises a horizontal upper section, a curved transition section and a lower section forming a leg, characterized in that the horizontal upper sections of the four support elements are arranged crosswise and connected in a central zone by means of a central connecting unit including a central connecting body and an upper clamping element connected to each other by threaded fasteners, wherein in the central connecting body and in the upper clamping element there are lateral receiving sections for accommodating the end parts of the horizontal upper sections of the support elements, wherein the central connecting body and the upper clamping element are designed with the possibility of mutually tightening and fixing the end parts of the horizontal upper sections of the support elements in the central zone.

2. A chair support according to claim 1, characterized in that the central connecting body and the upper clamping element have a geometrically similar shape.

3. A chair support according to claim 1, characterized in that the central connecting body and the upper clamping element are arranged in a mirror image relative to the plane of placement of the horizontal upper sections of the support elements.

4. A chair support according to claim 1, characterized in that the central connecting body and the upper clamping element are made in the form of two mating body elements, each of which contains lateral receiving sections for accommodating at least part of the end parts of the horizontal upper sections of the support elements.

5. A chair support according to claim 1, characterized in that part of the end parts of the horizontal upper sections of the support elements are placed in the lateral receiving sections of the central connecting body, and the other part of the end parts of the horizontal upper sections of the support elements are placed in the lateral receiving sections of the upper clamping element.

6. A chair support according to claim 1, characterized in that the end parts of two oppositely located support elements are placed in the lateral receiving sections of the central connecting body, and the end parts of two other oppositely located support elements are placed in the lateral receiving sections of the upper pressure element.

7. A chair support according to claim 1, characterized in that the side receiving sections are designed to cover the end portions of the horizontal upper sections of the support elements from at least two sides.

8. A chair support according to claim 1, characterized in that the end parts of the horizontal upper sections of the support elements are clamped between the tightened central connecting body and the upper clamping element, limiting their displacement in the vertical and horizontal directions.

9. A chair support according to claim 1, characterized in that the central connecting body and the upper clamping element are provided with aligned fastening holes through which threaded fastening elements are passed.

10. A chair support according to claim 1, characterized in that the central connecting body and the upper clamping element, when tightened together, form a closed volumetric connecting block.

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