PROPULSION DEVICE FOR MOVING A WHEELCHAIR

Description

PROPULSION DEVICE FOR THE MOVING A WHEELCHAIR DESCRIPTION FIELD OF INVENTION The present invention falls within the scope of the creation of devices for the motorization of wheelchairs for disabled people. In particular, this The invention relates to a propulsion device for the motorization of a wheelchair for a disabled person. The invention also relates to a wheelchair comprising said device according to the invention. STATE OF THE ART The existence of wheelchairs for disabled people that are manually pushed is known, where such pushing is exercised directly by the person sitting in the wheelchair or by an accompanying person. In order to To eliminate this physical effort, motorized wheelchairs have been proposed, i.e. wheelchairs equipped with an electric motor, which provides the force necessary to move the wheelchair forward, and a control unit that allows the disabled person to control this progress. In a motorized wheelchair the control unit, the electric motor and all the components that allow the transfer of the driving torque from the engine to the wheels and are installed on board the wheelchair itself impacting strongly and therefore disadvantageously on its weight overall. In addition to this, a motorized wheelchair necessarily has a structure rigid, i.e. not foldable, unlike what can happen in the case of a manual push wheelchair. To overcome these drawbacks, in recent years devices have been proposed propulsion which can be removably connected to the wheelchair's supporting frame. In particular, a device of this type comprises a steering column in which is inserted a column that supports a handlebar at the top and which is then attached to it associated with a fork at the bottom. A wheel that integrates a pivot is attached to this latter. electric motor that makes it a driving force. The electric motor is powered by a battery installed, together with a control unit, on the steering head. The advancement of the wheelchair is controlled by the person sitting in the wheelchair by means of controls (brake, accelerators) associated with the handlebars. Examples of these devices are shown in EP 2810633 and in patent IT 1417628. In In particular, in the solutions described in these documents the device includes a frame U-shaped, i.e. comprising a crosspiece and two arms, each of which can be connected to a front upright of the wheelchair's supporting frame. The U-frame is connected to the steering column through a flange, integral with the steering head, coupled to a fork integral with the cross member of the U-frame. More precisely, the fork is hinged to the flange through a first pin and is placed, at least partially, between the two opposite plates defining the fork. A second pin allows you to adjust the inclination of the frame with respect to the seat tube. using a plurality of holes defined on the flange and on the fork. The connection in question It involves the use of play elimination devices mounted on the fork and acting on the flange to eliminate the play between the latter and the fork. Further examples of removable propulsion devices are shown in patent applications. IT20200000003789 and IT20180010144. In particular, these documents show different connecting means provided for connecting the U-frame to the steering head of the device. In the solution shown in IT20200000003789, for example, the use of a flange is foreseen connected to the steering head where this flange supports a drum comprising two faces of parallel and specular lines with respect to a central plane of the device. In correspondence with these Two connecting pins are arranged on the parallel faces. On the crosspiece of the U-frame there is a a pair of brackets each comprising a pair of forked ends capable of mate with the connecting pins of one of the parallel faces of the drum. This The solution also includes the use of means to eliminate the play between the drum and the forks in order to stabilize the coupling. In the solution shown in IT20180010144 the connection between the steering head and the frame U-shaped is made through cylindrical sleeves also providing in this case screw tightening means and means for recovering the play between the mating parts. The Applicant has found that the above-described solutions proposed so far to connect the intermediate frame to the steering column are extremely complex requiring a remarkable number of components. In this regard, it is observed, for example, how substantially all the solutions described require the use of specific means to recover the play between the connecting components. In general, the complexity of this solution impacts unfavorably on the final costs of construction. Furthermore, this complexity also affects the weight overall propulsion device, thus limiting its performance. the drawback is the large size of the propulsion device when it is not in use, that is, when it is not connected to the wheelchair. SUMMARY The aim of the present invention is therefore to provide a propulsion device for motorize a wheelchair for the disabled that allows you to overcome or at least mitigate the inconveniences indicated above. Within this scope, a first object of the present invention is to provide a propulsion device for motorizing a wheelchair for disabled people having a less complex and more easily realisable configuration than that of the solutions notes. Another purpose, linked to the previous one, is to provide a propulsion device for motorize a wheelchair where the connecting components do not require specific means for game recovery. Yet another object is to provide a propulsion device for powering a wheelchair for the disabled that takes up little space when not in use. Not least, the present invention aims to provide a propulsion device that is reliable and easy to produce at competitive costs. The above mentioned task and purposes can be achieved through a propulsion device of a wheelchair for disabled persons according to claim 1. Preferred embodiments of the invention are specified in the dependent claims. More precisely, the said task and the said purposes are achieved through a device of propulsion system comprising a steering head in which a column is inserted which supports a handlebar and a fork connected at the bottom to the seat tube and to which a pivot is attached wheel. The device also comprises a drive unit comprising an electric motor operationally connected to the wheel to determine its rotation. The device comprises also an intermediate frame which can be removably connected to a load-bearing frame of the wheelchair and a connecting unit that adjustably connects the intermediate frame to the steering head. The connection unit includes a first bracket integral with the steering head steering and a second bracket integral with the intermediate frame. The first bracket comprises a first coupling portion provided with first engagement elements and the second bracket comprises a second coupling portion provided with second engagement elements. The first elements of commitment are engageable with said second elements of commitment and said unit of connection comprises an elastic element placed between the mating portions and a clamping group which in an activated condition develops, in opposition to the element elastic, a force such as to cause the mating portions to engage and such as to maintain this condition of commitment. In accordance with a preferred embodiment, the intermediate frame has a substantially U-shaped and includes a crosspiece and a pair of arms connection between opposites, in which each arm can be connected to a frame upright wheelchair carrier. Preferably, the crosspiece comprises a central portion and two lateral portions each of which integral with a corresponding one of said arms, in which each lateral portion is telescopically connected to the central portion, called crosspiece, including means of locking to lock each lateral portion with respect to the central portion. In accordance with a preferred embodiment, the first elements of engagement comprise a plurality of protrusions that develop in relief from a flat surface of the first portion of coupling and the second engagement elements comprise a plurality of compartments which are develop from a flat surface of the second mating portion, in which said spaces have a shape geometrically conjugated to that of said protrusions, called first mating portion engaging the second mating portion to following the insertion of said protrusions into said spaces. In accordance with a preferred embodiment, said clamping group comprises a pin central one that passes through the mating portions and emerges with respect to the second portion of coupling. This central pin is fixed to the first coupling portion. The group clamping comprises at least one clamping lever and a stop bushing arranged between the clamping lever and the second coupling portion. This clamping lever comprises a cam end acting on the second coupling portion through the bushing feedback. This clamping lever can be rotated between a release position and a locking position. tightening following which the mating portions maintain each other busy. Preferably, the first mating portion comprises a first seat in which there is at least partially housed said elastic element and / or the second coupling portion preferably comprises a second seat in which the said is at least partially housed elastic element. According to a possible embodiment, the first elements of commitment of the first portion of coupling and the second engagement elements of the second coupling portion they are configured to allow coupling according to at least a first modality commitment and at least one second mode of commitment characteristic of a condition of use and a condition of non-use of said device. Preferably, the second mode of engagement is such that the intermediate frame is arranged on a reference plane that is substantially parallel to a development axis of the said steering head. In accordance with a preferred embodiment, the connection unit comprises means of guide to guide the rotation of the second bracket relative to the first bracket around an axis reference center defined by a central pin of the clamping group. Preferably, such guiding means comprise a pin connected to the first bracket and which emerges towards the second bracket on the same side as the first elements of engagement, and a seat defined in the second bracket by the part where said second engagement elements are defined, said seat developing in the shape of a circular arc coaxially to said central axis of reference. Said pin is at least partially housed in said seat. According to one possible embodiment, each connecting arm comprises a fixed-angle clamp, wherein said clamp comprises a first body and a second body body connected through a plurality of connecting screws that configure a releasable coupling. The first body defines a first through cavity suitable for being crossed by a relative arm of the intermediate frame. The clamp also includes a screw tightening to removably fix the first body to the relative arm. Each of the bodies have a semi-cylindrical portion geometrically conforming to a surface of a upright of the wheelchair. These bodies can be positioned on opposite sides of the upright and fixed to the latter through the said connecting screws so that the upright itself remains tightened between the semi-cylindrical portions of the two bodies. LIST OF FIGURES Further features and advantages of the present invention will become more clear. from the description of preferred, but not exclusive, embodiments of a device propulsion according to the invention, illustrated by way of example in the attached drawings, in which: - figures 1 and 2 are perspective views from different observation points of a wheelchair comprises a device according to the present invention; - figures 3 and 4 are perspective views from different observation points of a group of components of the device of figures 3 and 4; - Figures 5 and 6 are perspective views of the assembly of components in Figures 3 and 4 each relating to a possible connection method between the components themselves; - Figure 7 is a side view of the wheelchair in Figures 1 and 2; - Figure 8 is a view of a device according to the invention in a non-operating condition use; - Figures 9, 10 and 11 show steps in the method of connecting a device according to the invention of a wheelchair; - Figures 12 and 13 are views of a component of a device according to the invention; The same numbers and reference letters in the figures identify the same elements or components. DETAILED DESCRIPTION With reference to the above figures, the present invention relates to a device for propulsion 1 which can be removably connected to a wheelchair 2 to allow its movement, that is, to move it without physical effort on the part of the disabled person or by a companion. Figures 1, 2 and 7 show a possible, and therefore not exclusive, embodiment of a wheelchair 2 comprising a device 1 according to the invention. In general, the device 1 according to the invention can be connected to a wheelchair 2 provided with a load-bearing frame 21 which supports a pair of rear wheels 22A, 22A, of larger size, and a pair of 23A front wheels, 23A steering size markedly lower than the rear wheels 22A, 22B. The load-bearing frame 21 supports a seat 24 and comprises at least one pair of front uprights 201 to which the device can be connected of propulsion 1 (hereinafter also referred to as device 1) according to a preferred mode described below. The wheelchair 2 also includes a pair of footrests 28 to allow the disabled person to rest their feet while walking. The device 1 according to the invention comprises a steering tube 11 which extends along a development axis 100. Inside the steering head 11 there is a column 12 which supports a handlebar 13 at the top. At the lower end of the steering tube 11 is connected to a fork 14 to which a wheel 4 is pivoted. The handlebar 13 allows steering of the wheel 4 and therefore the driving of the wheelchair 2. Preferably means are provided for limit the steering of wheel 4 relative to the steering head 11, i.e. to allow wheel 4 to rotate by a predetermined angular interval. In other words, such means prevent the wheel 4 to be able to rotate completely around the development axis 100 of the steering head 11. In the embodiment shown in the figures, these means are provided with a pin 91 (indicated in figure 3) integral with the steering tube 11 and whose end is inserted in a groove (not visible in the figures) defined on a transverse part 92 (indicated in Figure 2) of the fork 14, where this groove is concentric to the development axis 100. The device 1 according to the invention also comprises a drive unit 18 which includes a electric motor M operationally connected to wheel 4. As shown in the figures, of Preferably the electric motor M is incorporated into the hub of wheel 4 and is powered by a battery B connected to the steering head 11. The drive unit 18 also includes a control unit C also connected, directly or indirectly, to the steering head 11. Preferably, the The M engine is configured to rotate wheel 4 in both directions to allow forward travel. of device 1 and also its reverse gear. The activation of the engine M is governed through controls associated with the handlebars 13. The device 1 according to the invention comprises an intermediate frame 30 (hereinafter referred to as also with the term frame 30) through which the device 1 can be connected to the supporting frame 21 of the wheelchair 2, in particular to the two front uprights 201 symmetrical with respect to a longitudinal plane of the wheelchair itself. The intermediate frame 30 is connected to the steering tube steering 11 through a connection unit 40 which allows the mutual selection inclination of the two connected components (intermediate frame 30 and steering head 11) between a finite number of possible inclinations. As shown in the figures, preferably the intermediate frame 30 has a conformation substantially U-shaped in which a crosspiece 31 and a pair of arms 32 are identified connection between them opposite. The two arms 32 have a mirror structure with respect to a reference plane R1 passing through the development axis 100 of the steering head 11. Each connecting arm 32 can be connected to one of the front uprights 201 of the wheelchair 2 through means of attachment. In one of their possible, and therefore non-exclusive, forms of implementation, such coupling means comprise a fixed-angle clamp 34, i.e. a clamp configured to connect the two parts (an arm 32 and an element 201) so that the same have a fixed, pre-set inclination, i.e. not adjustable. This terminal 34 is further forward better described with reference to Figures 12 and 13. In accordance with a preferred embodiment (visible in figures 3 and 4), the crosspiece 31 of the frame 30 comprises a central portion 31A and two lateral portions 31B each which are integral with a corresponding one of said arms 32. In particular, each lateral portion 31B is telescopically connected to said center portion at 3 l 1A so as to adjust the distance between said arms 32. To this end, the crosspiece 31 is provided with locking means 31C for lock each lateral portion 31B to said central portion 31. In the embodiment shown in the figures, such locking means 31C comprise a plurality of grub screws which act on the lateral portions 31B fixing their position with respect to the central portion 31A. According to the present invention, the connecting unit 40 is therefore interposed between the frame intermediate 30 and the steering head 11. In particular, the connecting tube 40 comprises a first bracket 41 integral with the steering head 11 and a second bracket 42 integral with the crossmember 31 of the intermediate frame 30. The first bracket 41 comprises a first coupling portion 41A including first engagement elements 411 configured to engage with other elements of commitment 421 (or second commitment elements 421) defined on a portion 42A of coupling (also called second portion 42A) of the second bracket 42. The connecting unit 40 also comprises an elastic element 47 (preferably a (coil spring) placed between the two coupling portions 41A, 42A. This element is elastic 47 tends to separate the two coupling portions 4A, 1 42A. The unit of connection 40 further comprises a clamping assembly 50 which in a condition of activation develops a force, in opposition to said elastic element 47, such as to cause the engagement is such as to keep the two coupling portions 41A, 42A engaged, thus ensuring the connection between the steering head 1 and the intermediate frame 30. When the clamping group 50 is not activated, the engagement between the two coupling portions 41A, 42A is missing and the intermediate frame 30 becomes movable with respect to the steering head 11. In accordance with a possible embodiment visible in the figures, f the first bracket 41 is connected (preferably welded) to the steering head 11 on a rear portion thereof, i.e. on a portion that is facing wheelchair 2 in a condition of use of device 1 as visible, for example, in Figure 7. The battery B of the drive unit 18 is preferably connected to a front portion of the steering head 11, hence in a position opposite to that of the first bracket 41 (see for example Figure 7). With particular reference to Figure 3, the first engagement elements 411 of the first portion of coupling 41A are defined by a plurality of protrusions that develop in relief from a flat surface 412. These protrusions are preferably shaped like a circular sector and are arranged around a central reference axis 450. From the side of said flat surface 412, the first bracket 41 comprises a first seat 455 in which it is partially arranged the elastic element 47. Preferably, this first seat 455 is circular and coaxial with the axis reference center 450. With reference to Figure 4, the second engagement elements 421 provided on the second portion of coupling 42A are defined by a plurality of geometrically shaped compartments conjugated to those of the protrusions defined on the first coupling portion 41A, which develop in recess in a flat surface 422. Therefore, also said spaces preferably have a circular sector shape and are arranged around the said central axis of reference 450. Preferably, from the side of the flat surface 422 in which said compartments, the second bracket 42 comprises a second seat 456 in which at least one partially the elastic element 47 (see Figure 4). This second seat 456 is also preferably circular and coaxial to said central reference axis 450. The connection between the two plates 41, 42 therefore occurs following the insertion of the protrusions (first elements of commitment 411) in the spaces (second elements of commitment 421). In their complex, the two coupling portions 41A, 42A configure a sort of joint front tooth graft. In this regard, as better specified below, the configuration of the engagement elements 411, 421 of the mating portions 41A, 42A allows different engagement configurations each of which establishes a different inclination of the steering head 11 with respect to the intermediate frame 30 and vice versa. Still referring to figures 3 and 4, the clamping group 50 comprises a central pin 55 (or through pin 55) which passes through the two coupling portions 41A, 42A and which emerges with respect to the coupling portion 42A of the second bracket 42. The pin 55 is fixed firmly (preferably screwed) to the first bracket 41 at its first end 55A. Preferably, this central pin 55 is coaxial with the reference axis 450 and the elastic element 47 is arranged around the same central pin 55. The clamping assembly 50 comprises a clamping lever 56 and a stop bushing 58. arranged between the clamping lever 56 and a surface of the second coupling portion 42A opposite to the surface 422 from which said spaces develop (second elements of engagement 421). The clamping lever 56 includes a cam end 56A which pivots in correspondence of a second end of the through pin (opposite to said first end 55 55A). The cam portion 56A acts on the stop bushing 58 and through this on the second coupling portion 42A. The clamping lever 56 can therefore be rotated between a release position and a clamping position around a rotation axis 420 substantially orthogonal to the central reference axis 450. During the movement from the from the release position to the tightening position, due to its cam end 56A, the lever 56 exerts, via the bushing 58, a force on the coupling portion 42A of the second bracket 42 in contrast to the thrust exerted by the elastic element 47. In a first phase of rotation of the lever 56 the two coupling portions 41A, 4 2A engage reciprocally. Always by virtue of its cam end 56A, upon reaching the clamping position, the clamping lever 56 maintains the engagement between the portions of coupling 41A, 42 A until it is manually returned to the position of release. Therefore, the clamping assembly 50 is “activated” when the clamping lever 56 is brought into the tightening position and as long as the tightening lever 56 itself maintains this position position. In accordance with a preferred embodiment, the first engagement elements 411 of the first bracket 41 and the second engagement members 421 of the second bracket 42 are configured so to allow the two brackets 41, 42 to be coupled according to at least a first method commitment following which the intermediate frame 30 is placed on a reference plane (indicated by 501 in Figure 7) substantially inclined (preferably orthogonal) to the axis of development 100 of the column 12. As evident from Figure 7, the first mode of engagement is characteristic of a condition of use of the device 1, that is when it is connected to the wheelchair 21 load-bearing frame. Referring to Figure 8, the first engagement elements 411 of the first bracket 41 and the second engagement elements 421 of the second bracket 42 are configured to allow a coupling of the two brackets 41, 42 also in accordance with a second engagement mode for which the intermediate frame 30 is arranged on a reference plane 501 which is substantially parallel to the development axis 100 of the column 12. This mode of engagement is characteristic of a condition of "non-use" of the device 1, that is when the same is not is connected to the wheelchair 2. With reference to Figures 9 and 10, first engagement elements 411 of the first bracket 41 and the second engagement elements 421 of the second bracket 42 are configured to also engage according to a third possible mode of engagement whereby the intermediate frame 30 assumes, with respect to the steering head 11, an intermediate inclination between the other two possible inclinations obtainable with the other two modes of commitment described above. This third mode of engagement can be usefully employed to facilitate the engagement of the device 1 to wheelchair 2 as better described below. The selection of the engagement mode of the two brackets 41, 42 is made when the group clamping lever 50 is deactivated, i.e. when the clamping lever 56 occupies the release position (visible in Figure 10). In this condition, the two coupling portions 41A, 42A of the respective brackets 41, 42 are spaced apart by the effect of the elastic element 47. Therefore, the first bracket 41, and therefore the intermediate frame 30 integral with it, can be rotated with respect to the second bracket 42 (i.e. with respect to the steering head 11) around the central axis 450 of reference, i.e. around the central pin 55 of the spoke group if 50 coaxial to this axis central 450. In this regard, the connection unit 40 preferably comprises guide means 81-82. designed to guide the rotation of the first bracket 42 with respect to the first bracket 41 (or vice versa) around the central reference axis 450. With reference to figures 3 and 4, in one of their possible embodiment, such guide means 81-82 comp make a pin 81 connected to the first bracket 41 and which emerges, towards the second bracket 42, from the same face 412 from which the first elements of engagement 411 (protrusions) emerge. The guiding means also include a seat 82 defined in the second bracket 42 from the side / face where the second elements are defined of commitment 421 (spaces). In particular, this seat develops in a coaxial arc of a circle to the central reference axis 450. The pin 81 is partially housed in this seat 82 so that it acts as a guide element for the rotation of the first bracket 41 with respect to the second bracket 42. Figures 12 and 13 show a possible embodiment of the connecting means of the U-frame to the uprights 201 of the wheelchair 2. In particular, such connecting means include, for each arm 32 of the intermediate frame 30, a tilting clamp 34 fixed. The term “fixed inclination” indicates that terminal 34, following its tightening, establishes a single possible inclination for the intermediate frame 40 with respect to the front uprights 201 of wheelchair 2 and vice versa. Preferably, terminal 34 comprises a first body 34A and a second body 34B connected through a plurality of removable connecting screws 33 which configure a coupling releasable between the bodies themselves. The first body 34A defines a first cavity 35A passing through intended to be crossed by a relative arm 32 of the intermediate frame 30 (see Figure 12). The clamp 34 includes a clamping screw 39 (preferably with a knob head) which allows the first body 34A to be fixed in a removable manner to the relative arm 32. In By the way, loosening the clamping screw 39 allows, for example, to adjust the position of clamp 34 along the arm of intermediate frame 30. The two bodies 34A, 34B each have a geometrically shaped semi-cylindrical portion 37 conforming to the surface of a front upright 201 of the wheelchair 2. The two bodies 34A, 34B are positioned on opposite sides of the front upright 201 through the screws removable connection 33 indicated above so that the same upright remains tightened the two semi-cylindrical portions 37. Therefore, the removable connecting screws 33, in addition to connecting the two bodies 34A, 34B, fix the position of the clamp 34 on the relative upright 201 of the wheelchair 2. In the embodiment shown in the figures, the through cavity 35A defined by the first body 34A has a longitudinal axis 401 orthogonal to the axis 402 of the semi-cylindrical portions 37 intended to contact the relevant upright. However, it is possible to foresee a different inclination between the axes 401, 402 just indicated. Furthermore, in a further possible embodiment (not shown in the figures), the first body 34A may comprise two hinged portions for ease of connection and removal of the clamp 34 from the relative arm 32 of the intermediate frame 30. In this case, each portion may define a part of the through cavity 35A. It may also be a connecting screw is provided which connects the two portions of the first body 34A together so as to tighten them around the relative arm 32 of the intermediate frame 30. With particular reference to figures 7 to 11, the method by which the propulsion device 1 is connected to the wheelchair 2, in particular to the uprights front 201 of its supporting frame 21. As indicated above, in a non-used condition, the intermediate frame 30 is connected to the steering head 11 as shown in Figure 8, i.e. in so as to take up minimal space. To connect the intermediate frame 30 to the wheelchair 2, the clamping group 50 is deactivated to vary the engagement mode between the portions of connection 41, 42. The latter are coupled again in the third possible mode of engagement described above. The clamping group 50 is then re-engaged activated. With reference to figure 9, through the two terminals 34, the two arms 32 of the frame intermediate 30 are connected to the respective front uprights 201 of the wheelchair 2. Subsequently the clamping group 50 is deactivated (unlocked) so as to cause the rotation of the drive unit 18 around the central reference axis 450 of the drive unit tightening 50 until wheel 4 reaches the support surface PO. At this point, acting upon appropriate command, the electric motor M is activated in the “reverse” mode in so as to cause the drive unit 18 to move backwards towards the wheelchair 2. This reverse gear determines the relative rotation of the intermediate frame 30 with respect to the steering head 11 and at the same time lifting the front part of the wheelchair 2 (as shown in Figure 11). Following the rotation of the frame 30, the two coupling portions 41A, 42A (separated by the deactivation of the release of the clamping lever 58) rotate mutually until they reach a position where they can mate in accordance with the first mode of engagement indicated above. At this point, the clamping group 50 is activated in so as to mutually engage the mating portions 4 1A, 42A and so as to keep this coupling stable. The propulsion device 1 according to the invention therefore allows the task to be achieved and the intended purposes. In particular, the connecting unit 40 provided between the intermediate frame 30 and the steering head 11 is constructionally simple and at the same time extremely effective. Advantageously, the propulsion device 1 according to the invention has a compact size limited in the condition of non-use, where even such limited bulk is permitted by the particular configuration of the connection unit 40.

Claims

CLAIMS 1) Propulsion device (1) for moving a wheelchair (2) for a disabled person, wherein said device (1) comprises: a steering tube (11) in which a steering column (12) is inserted which supports a handlebar (13); a fork (14) connected below to said steering column (12) and to which a wheel (4) is hinged; a drive unit (18) comprising an electric motor (M) operatively connected to said wheel (4) to determine its rotation; an intermediate frame (30) which can be removably connected to a load-bearing frame (21) of said wheelchair (2); a connecting unit (40) which adjustably connects said intermediate frame (30) to said steering head (11), characterised in that said connecting unit (40) comprises a first bracket (41) integral with said steering head (11) and a second bracket (42) integral with said intermediate frame (30),wherein said first bracket (41) comprises a first coupling portion (41A) provided with first engagement elements (411) and wherein said second bracket (42) comprises a second coupling portion (42A) provided with second engagement elements (421), wherein said first engagement elements (411) are engageable with said second engagement elements (421), said connection unit (40) comprising an elastic element (47) interposed between said coupling portions (41A, 42A) and a clamping assembly (50) which, when activated, develops, in opposition to said elastic element (47), a force which causes the engagement of said coupling portions (41A, 42A) and which keeps said portions engaged. 2) Device (1) according to claim 1, wherein said intermediate frame (30) has a substantially U-shaped shape and includes a crosspiece (31) and a pair of connecting arms (32) opposite each other, wherein each arm (32) can be connected to an upright (201) of said load-bearing frame (21) of said wheelchair (2). 3) Device (1) according to claim 2, wherein said crosspiece (31) comprises a central portion (31A) and two lateral portions (31B) each of which is integral with one of said arms (32), wherein each lateral portion (31B) is telescopically connected to said central portion (31A), said crosspiece (31) comprising locking means (31C) for locking each lateral portion (31B) with respect to said central portion (31A). SAV04289 / IT 4) Device (1) according to any of claims 1 to 3, wherein said first engagement elements (411) comprise a plurality of protrusions which develop in relief from a flat surface (412) of said first coupling portion (41A) and wherein said second engagement elements (421) comprise a plurality of spaces which develop from a flat surface (422) of said second coupling portion (42A), wherein said spaces have a shape geometrically conjugated to that of said protrusions, said first coupling portion (41A) engaging with said second coupling portion (42A) following the insertion of said protrusions into said spaces. 5) Device (1) according to any of claims 1 to 4, wherein said clamping assembly (50) comprises a central pin (55) which passes through said coupling portions (41A, 42A) and which emerges with respect to said second coupling portion (42A), said central pin (55) being fixed to said first coupling portion (41A), said clamping assembly (50) comprising at least one clamping lever (56) and a stop bushing (58) disposed between said clamping lever (56) and said second coupling portion (42A), said clamping lever (56) comprising a cam end (56A) which acts on said second coupling portion (42A) through said stop bushing (58), said clamping lever (56) being rotatable between a release position and a clamping position following which said coupling portions engage. (41 A, 42A) remain mutually engaged. 6) Device (1) according to any of the preceding claims, wherein said first coupling portion (41A) comprises a first seat (455) in which said elastic element (47) is at least partially housed and / or wherein said second coupling portion (42A) comprises a second seat (456) in which said elastic element (47) is at least partially housed. 7) Device (1) according to any of the preceding claims, wherein said first engagement elements (411) of said first coupling portion (41A) and said second engagement elements (421) of said second coupling portion (42A) are configured to engage according to at least a first engagement mode and according to at least a second engagement mode characteristic respectively of a condition of use and a condition of non-use of said device (1). 8) Device (1) according to claim 7, wherein said second engagement mode is such that said intermediate frame (30) is arranged on a reference plane (501) which SAV04289 / IT turns out to be substantially parallel to a development axis (100) of said steering head (11). 9) Device (1) according to any of claims 1 to 8, wherein said connecting unit (40) comprises guide means (81-82) for guiding the rotation of said second bracket (42) relative to said first bracket (41) around a central reference axis (450) defined by a central pin (55) of said clamping assembly (50). 10) Device (1) according to claim 9, wherein said guiding means (81-82) comprise a pin (81) connected to said first bracket (41) and emerging towards said second bracket (42) from the same side as said first engagement elements (411), and a seat (82) defined in said second bracket (42) from the side in which said second engagement elements (421) are defined, said seat (82) developing in the shape of a circular arc coaxially with said central reference axis (450), said pin (81) being at least partially housed in said seat (82). 11) Device (1) according to any of claims 1 to 10, wherein each connecting arm (32) comprises a fixed-angle clamp (34), said clamp (34) comprising a first body (34A) and a second body (34B) connected through a plurality of connecting screws (33) which configure a releasable coupling, wherein said first body (34A) defines a first through cavity (35A) suitable to be passed through by a relative arm (32) of said intermediate frame (30), said clamp (34) comprising a tightening screw (39) to removably fix said first body (34A) to said relative arm (32), and wherein each of said bodies (34A, 34B) has a semi-cylindrical portion (37) geometrically conforming to a surface of an upright (201) of said wheelchair (2), said bodies (34A,34B) being positionable on opposite sides of said upright (201) to be fixed to the latter through said connecting screws (33) so that the upright (201) itself remains clamped between said semi-cylindrical portions (37).,