FR2841462A1 - Lightweight wheelchair has attachable module with single steerable wheel and two arms for converting it to all-terrain use - Google Patents

Abstract

The wheelchair (1), comprising a frame (3) with a seat, two main propulsion wheels (4) and two small front steerable wheels (7), has an attachable module (2) to give it all-terrain use. The module has a large front steerable wheel (12) mounted on a structure (11) with two arms (10) that attach to the front uprights (5) of the wheelchair frame by quick-release clamps (14) so that its small steerable wheels are held off the ground.

Description

The present invention relates to the design and production of a module

  transformation of a wheelchair from a city wheelchair configuration into a so-called all-terrain wheelchair configuration, allowing the movement of the wheelchair over uneven terrain. The invention applies in particular to so-called active light and ultra-light wheelchairs, that is to say intended for active people who move alone outdoors. These are people with reduced mobility who, deprived of the use of their legs, temporarily or permanently, and forced to use a wheelchair for their movements, nevertheless lead a normal and active life. This implies being able to perform all the gestures of daily life independently, in particular the transfer from the car to the wheelchair and vice versa. The wheelchairs used by active people are therefore light, easy to handle and often foldable. The invention can however be extended to all kinds of wheelchairs, including those of the hospital wheelchair type. Classic wheelchairs, known as city wheelchairs, are provided with a chassis supporting a backrest and a seat, two large removable rear drive wheels, and one or two small front steering wheels permanently fixed on fixed uprights of the chassis. An example of such a wheelchair is described in patent application WO 97/00657. These chairs are intended to be used on hard and flat floors, and are

  totally unsuitable for irregular terrain.

  However, active people may in particular wish to walk on such land, for example on a dirt road in the forest or around a lake, and this independently. A specific chair, known as all terrain, is therefore necessary for this purpose. It is fitted with all-terrain type wheels, two at the rear and one in the central position at the front, which are larger than the usual wheels and whose tires are notched and thicker. By the very fact of their specificity, all-terrain armchairs, on the other hand, are much less manageable than city armchairs; they are also more bulky, and are therefore unusable for example in the house. In addition, they do not allow direct transfer of the user from his car. Active people wishing to move on irregular terrain therefore have no other solution at present than to obtain two wheelchairs, a city chair and an all-terrain chair, with the disadvantages of cot, clutter and complications that

that implies.

  The object of the present invention is to allow active people with reduced mobility to walk on all types of terrain, including irregular terrain, without it being necessary for them to have two different wheelchairs. Thus, the invention proposes a removable module which makes it possible to transform a city wheelchair to make it usable on

  all types of terrain, including uneven terrain.

  Another essential objective of the invention is to keep active disabled people their autonomy of action, while ensuring that the transformation module is easy and practical to use, without requiring external assistance, for a person.

  while sitting on his chair.

  The removable module for transforming a city wheelchair configuration into an all-terrain wheelchair configuration is intended to equip any wheelchair essentially comprising a chassis supporting a seat for a disabled person, a set of rear driving wheels. and a set of small front steering wheels permanently mounted on the uprights of the chassis. It adapts equally to wheelchairs with drive system

automatic or manual.

  The module according to the invention is placed in front of the chair, 30 connected to the fixed uprights thereof. Here and throughout the rest of

  the present description, the module and its various elements are defined with respect to this normal position of use, in

  whereas the wheelchair is oriented in its usual direction

  advancement, going from back to front.

  The module comprises a large front steering wheel which is arranged along an axis of symmetry of the chair, mounted on a structure having branches respectively connectable to the uprights of the chassis, and means placed under the control of the person to ensure the locking of the chair in a so-called all-terrain position, reached by tilting the chair backwards. The off-road position is defined by the fact that the wheelchair is only supported on the rear wheels and on the large front steering wheel, the set of small front steering wheels being 1o sufficiently raised so as not to come into contact with the roughness of the ground . This position can be reached for example by transferring the weight of the user, while sitting on the

  armchair, from seat to back.

  The module according to the invention thus advantageously makes it possible to retract the small front steering wheels in order to put the chair on three wheels, namely its two rear driving wheels and a large steering wheel carried by the module, which is in position central to the front of the chair. This last point provides stability to the chair, which is

  particularly advantageous on uneven terrain.

  In preferred embodiments of the invention, the large front wheel is of the all-terrain wheel type, equipped with a thick notched tire and more resistant to punctures than normal, so as to give the wheelchair more efficiency in its 25 movements, and in particular better grip on soft soil. The module can also optionally be associated with a set of all-terrain type wheels adaptable to the chassis to replace the usual rear driving wheels. This exchange 30 is easy to carry out, since for most of the armchairs, the large rear wheels are removed to allow the folding of the armchair before it is loaded into a car. It then suffices for the user, when unfolding the chair, when he knows that he will have to use it in an all-terrain configuration, to mount on the chassis, in place of the usual large wheels, the play large off-road wheels usable in conjunction with the module. In preferred embodiments of the invention, these off-road wheels

  are larger in diameter than the usual rear wheels.

  In the case of armchairs with manual drive by the user, they are in particular each equipped with one hand

  current allowing this training.

  In this way, we obtain an armchair similar to all-terrain armchairs, while achieving the financial savings of

the purchase of a second chair.

  Another advantage of the invention is the significant gain in terms of space it provides, since it is no longer necessary to store, or even transport, two different armchairs, but only one armchair and its transformation module, possibly accompanied by a set of large

all terrain wheels.

  In order to accentuate this particularly advantageous result, in preferred embodiments of the invention, the module is also designed so as to be foldable, so that it generates a minimal and light footprint so that it can be handled more easily. Thus, according to a secondary characteristic of the invention, the module is entirely made of low density materials. Additional Objectives and Benefits of the Invention

  will appear further during the description of the modes of

  preferred realization of the module object of the invention.

  According to a secondary characteristic of the invention, the branches are connectable to the fixed uprights of the transversely pivoted chair, around a horizontal axis perpendicular to the direction of advancement of the chair. The module comprises a locking device associated with each of the branches, operable between a position of free pivoting of the branch, facilitating the installation and removal of the module on the chair, and an armed position allowing the automatic locking of the pivoting

  of the branch when the wheelchair reaches the all-terrain position.

  Thus, without moving from its sitting position on the chair equipped with the module according to the invention, the user need only arm the devices for locking the pivoting of the branches, then tilt the chair backwards to retract the small ones. front steering wheels. As soon as the all-terrain position is reached, the branches pivot pivoting takes place automatically, and the chair is frozen resting on the ground by its rear wheels and by the large front wheel carried by the module. The reverse maneuver, returning to the configuration of the city armchair, does not present any more difficulties: the locking devices are returned by the user to their position of free pivoting of the

  branches, and the chair is tilted forward so as to bring the small front wheels into contact with the ground. The module can then be detached from the chair.

  In preferred embodiments of the invention,

  each locking device comprises a finger movable in translation parallel to the pivot axis of the branch. The finger is pushed towards the branch under the action of a spring, and it is able to fit into a slightly larger orifice 20 arranged in the branch and located opposite it when the chair is in the all position. courses. The locking device comprises means for controlling the translation of the finger against the spring, making it possible to remove the finger from the orifice.

  According to a secondary characteristic of the invention, each finger carries a stud which is perpendicular to it and which is able to move along a cam arranged so that the rotation of the finger on itself, under the effect of '' a rotational movement exerted by the person on a handle secured to the finger,

  causes the finger to move perpendicular to the branch.

  These latter characteristics give the module a very advantageous ease of use, since it suffices for the person to actuate the two handles to arm or disarm the device for locking the pivoting of the branches.

  For the same purpose of facilitating the manipulation of the module, according to preferred embodiments of the invention, each orifice is arranged in the branch at the end of an inclined face, which is advantageously arranged so as to facilitate the pivoting of the branch, when the finger is pushed under the action of the spring, until reaching the position in which the orifice is located opposite the finger. A minimal effort must therefore be provided by the user to bring the chair, once armed,

  in the all-terrain configuration.

  According to a secondary characteristic of the invention, each of the branches is connected at a rear end to a

  fixing device respectively to one of the uprights of the chassis.

  In preferred embodiments of the invention, the fixing device consists in particular of a clamp capable of enclosing the upright over its entire circumference and provided with

  means for locking it in its position enclosing the upright.

  According to a secondary characteristic of the invention, at the rear end of each branch, the transverse pivoting means, the device for locking this pivoting and the device for fixing to one of the fixed uprights of the chair are advantageously combined in the form of a compact control box. In preferred embodiments of the invention, the branches each extend at a rear end by a thinner plate in the form of a quarter disc, which is inserted into the control unit, by a slot arranged in this last, and which is pivotally hinged around a horizontal axis perpendicular to the direction of advancement of the chair when the module is placed on the latter in its normal position of use. The pivoting of the branch can then be locked by a device for locking the pivoting of the plate, included in the control box, and

  can be operated by the person seated on the chair.

  According to a secondary characteristic of the invention, each of the branches is connected at a front end to a steering column of the large front steering wheel, so as to pivot laterally, about an axis parallel to this steering column. The two branches of the module can therefore be freely moved apart or brought closer by their rear ends. This characteristic makes it possible to advantageously meet two objectives of the invention, namely on the one hand adaptability of the module to armchairs of all sizes, in particular from the point of view of the spacing between the two uprights to which the module io connects, and on the other hand a small footprint of the module in

its transport position.

  The invention will now be more fully described in the context of preferred characteristics and their advantages, with reference to Figures 1 to 5 in which: - Figure 1 shows a side view of a city wheelchair equipped with a module transformation; - Figure 2 illustrates a top view of the same module wheelchair assembly; - Figure 3 shows a side view of one of the module control boxes; - Figure 4 shows a sectional view along the axis C-C of the housing of Figure 3; - And Figure 5 shows a partial sectional view along the axis C-C of the housing of Figure 3, in its different positions

locking / unlocking.

  In Figure 1 is shown a so-called "city" wheelchair 1 equipped with a transformation module 2. The assembly is

  shown in its normal position of use, that is to say resting on the ground by its wheels and moving forward.

  The wheelchair 1 comprises a chassis 3 supporting a

seat and backrest.

  Two large rear driving wheels 4 are mounted

removable on the chassis 3.

  In preferred embodiments of the invention, these wheels 4 have a diameter greater than that of the usual rear wheels of city chairs, in particular between 500 and 700 mm, and preferably greater than 600 mm. They are also fitted with notched tires. A handrail, which is not shown in the figure, can be fixed to each of these wheels 4 to facilitate their manual drive by the user. However, the wheelchair equipped with the module can also be used with its usual rear wheels, but in a more limited way

  on very irregular terrain.

  The chassis 3 comprises, in its part located below the seat, two fixed transverse uprights 5 to which are connected one or two supports 6 of small front steering wheels 7. A footrest 8 is fixed to the lower end uprights 5. Two handles 9 extending the upper ends of the chassis 3 allow a second person to push the

chair 1.

  The module 2 is placed at the front of the chair 1. It is made of low density materials. It comprises two rigid longitudinal branches 10 which connect the transverse uprights 5 of the chair 1 and a front steering wheel 12 carried by the module 2.

  At a front end, the branches 10 are connected to a steering column 11 of the front wheel 12. This wheel 12 is equipped with a notched tire of the all-terrain type. In preferred embodiments of the invention, its diameter is between 450 and 550 mm, and preferably equal to about 508 mm, or 20 inches.

  At a rear end, each branch 10 is extended by a plate 13 of lesser thickness in the form of a quarter disc, which is partially inserted in a control box 14. The plate 13 is articulated, inside the box 14, pivotally transverse about an axis parallel to the steering column 11, and perpendicular to the direction of advance of the chair 1 (here perpendicular to the plane of the figure). The housing 14 further comprises a device for locking the pivoting of the plate 13,

controlled by a handle 15.

  Each housing 14 is fixed respectively to one of the transverse uprights 5 of the chair 1. The handles 15 are then located on the external lateral faces of the chair 1, so that they can be easily actuated by the person seated on the

chair 1.

  In this figure, the chair-module assembly is shown in its all-terrain position, that is to say resting

  only on the rear wheels 4 and on the large front wheel 12.

  The small front wheels 7 are raised and they do not come into contact with the ground. The chassis 3 is slightly inclined towards the rear relative to its normal position of use,

  and the seat is no longer in a horizontal plane.

  Given the large diameter of the front wheel 12, the arms 10 are slightly curved downwards in their rear part. In this way, when the front wheel 12 rests on the ground, the housings 14, located in the rear extension of the branches, are at a level which is both low enough to be able to be connected to the uprights 5, and high enough so that the

  handles 15 can be easily accessible to the person seated on the armchair 1.

  In an entirely advantageous manner, the module 2, and in particular the housings 14, the arms 10 and the wheel 12, are designed so as to make it possible to obtain a blocking of the pivoting of the arms in a position of the chair in which the small front wheels 7 are detached from the ground of a sufficient height so that they do not risk striking the roughness present on uneven floors. This height is preferably between 15

and 100 mm.

  FIG. 2 represents a top view of the module 2 and of the chair 1 illustrated in FIG. 1. For reasons of clarity,

  only the transverse uprights 5 of the chair 1 have been shown.

  As is perfectly illustrated in this figure, module 2 has an axis of symmetry A-A, which is the axis of symmetry

  of the wheelchair 1. The front wheel 12 is arranged along this axis.

  The branches 10 are brought closer to each other at their front end. They are connected at this end to the steering column 11 of the front wheel 12, each mounted so as to pivot laterally about an axis parallel to the steering column 11 (here perpendicular to the plane of the figure). This allows io quite advantageously that their rear ends can be separated or brought closer at will, with the consequence that the module can be fixed to the uprights 5 of all wheelchairs 1, whatever their spacing. The module according to the invention can thus advantageously be adapted to wheelchairs of all sizes. Furthermore, the rear ends of the branches 10 can also be brought very close to one another when the module 2 is not fixed to a chair 1. The module 2 then has a narrow longitudinal shape, it is not very

  bulky and its storage is facilitated.

  Each housing 14 comprises a device 16 for fixing to a fixed upright 5 of the chair 1. In the embodiment shown in the figure, it is a clamp comprising a tilting jaw and a fixed jaw, and which is placed around the upright 5 and enclose it around its entire circumference. It is provided with locking means 17, which are not shown on the

  figure, which make it possible to immobilize the tilting jaw in the clamping position of the clamp around the upright 5.

  The control unit 14 is shown more clearly

  detailed in side view in Figure 3.

  The plate 13 is inserted into the housing 14 in a slot 24 arranged over its entire height, without upper or lower limit. The depth of the slot 24 is substantially equal to the length of plate 13 inserted in the housing 14. The plate 13 is fixed in the housing 14 articulated at its upper corner inside the housing, rotating around an axis perpendicular to the direction of advancement of the chair, allowing the pivoting of the

branch 10.

  According to the embodiment of the invention shown in the figure, the locking means 17 of the clamp 16 consist of a hook which bears on the tilting jaw and keeps it tight around the upright 5. However, this representation n is not limiting of the invention, and any other means allowing a solid locking of the clamp 16 around the upright 5 can be used in the same way. Likewise, any fixing device 16 other than a clamp also comes within the scope of the invention. It is for example particularly advantageous, from the point of view of the adaptability of module 2 on all types of armchairs, to provide it with a fixing device 16 of adjustable dimension in

  depending on the diameter of the section of the upright 5.

  In FIG. 3 are shown in dotted lines a circular orifice 18 arranged in the plate 13, and a circular finger 19 of slightly smaller section, directed perpendicular to the slot 24 and to the plate 13. The finger 19 and the orifice 18 are concentric in the precise position of the branch 10 shown in this figure, which corresponds to the pivoting locking position of

plate 13.

  In an entirely advantageous manner, in the particular embodiment of the invention shown here, in this

  locking position, the plate 13 is in abutment over its entire height against the bottom of the slot 24, and it can only pivot upwards. The housing 14 and the plate 13 then form a compact assembly, which does not generate any discomfort for the user of the wheelchair.

  The handle 15 can be actuated in rotation about an axis perpendicular to the plate 13 and passing through the center of the section of the finger 19. The finger 19 is integral with the handle 15 and free to rotate, so that the pivoting of the handle 15 drives its

rotation on itself.

  A sectional view of the housing 14 along the axis C-C is

shown in figure 4.

  This view shows in more detail the device for locking the pivoting of the branch 10. It consists of the circular finger 19, integral in rotation with the handle 15, and which is located inside the housing 14. This finger 19 comprises two integral parts, one end 20 which is the end connected to the handle

  , and an end 21 which is located most inside the housing.

  The ends 20 and 21 are separated by a portion of larger

  diameter which forms a circular ring 22.

  The end 21 passes through a perpendicular cam 23, located between the ring 22 and the slot 24 formed in the housing 14,

  and it can reach this slot 24 and insert itself therein.

  A circular spring 26 surrounds the end 20 of the finger 19, and is applied to the ring 22 by exerting on it, by an elastic relaxation effect, a pressure force tending to push the finger

19 inside the slot 24.

  When the chair-module assembly is in the all-terrain configuration, resting on the rear wheels and on the large front wheel, the small front wheels 7 being retracted, the position of each branch 10 is such that the orifice 18 carried by the plate 13 is located in the slot 24 opposite the finger 19. Then, the end 21 of the latter is pushed by the spring 26 into the orifice 18. The pivoting of the plate 13, and therefore of the branch, is thereby blocked. Conversely, when the chair is not in an all-terrain configuration, the arms 10 form with the housings 14 an angle such that the orifice 19 is not located opposite

  finger 19. The latter is then pushed either inside the slot 24, or against the part of the plate 13 located facing it in the slot 24, depending on the position of the branch 10 at this given time.

  The end 21 of the finger 19 is provided with a stud 27 which

  is perpendicular and which can move along the cam 23.

  The displacement of the stud 27 on the cam 23 is shown

  in more detail in Figure 5.

  In the locked position, which is the first position illustrated in FIG. 5, the stud 27 is located in the low position on the cam 23, and the finger 19 is kept inserted in the orifice 18 under

spring action 26.

  When a rotational movement is exerted on the handle, the stud 27 moves upward along the cam 23, as shown in the intermediate position in Figure 5. A force opposite to that exerted by the spring 26 applies so on the

  finger 19, which has the effect of pulling it back out of the orifice 19.

  At the end of movement, when the handle 15 has been actuated by a quarter of a turn, the stud 27 is in the high position on the cam 23, and the finger 19 is entirely out of the orifice 18: the position is said to be unlocked , and the plate 13 is in a situation of

  free rotation. It is the third position shown in the figure.

  On the plate 13 is arranged an inclined face 28, which is arranged so that it is located on the path followed by the finger 19 on the surface of the plate 13 when the latter pivots about its axis to adopt the position required for off-road configuration. The inclined face 28 then advantageously facilitates the pivoting of the plate 13, when the finger 19 is pushed by the spring 26 in the slot 24, to the position in which the orifice

18 is located opposite finger 19.

  In practice, the use of the module according to the invention

proceed as follows.

  The user sits on chair 1, after having

  possibly mounted the rear wheel set 4 of the all-terrain type.

  He then takes hold of the module 2 by the boxes 14, and fixes one of the boxes 14 to one of the uprights 5 of the chair 1, by means of the fixing device 16. He spreads the arms 10 by a distance equal to the spacing between the two uprights 5, and fixes the second housing 14 on the second upright 5, at equal height with respect to the first. At this stage, the chair 1 is still resting on the rear wheels 4 and the small front wheels 7, and the large front wheel 12 carried by the module 2 is raised from the ground. The locking device is in the free pivoting position of the arms 10, with the stud 27 in the high position on the cam 23, and the finger 19

  moved back out of the slot 24. The spring 26 is then compressed. The user then arms the locking device, doing

  rotate each of the two handles 15 a quarter of a turn. The finger 19 rotates on itself and the stud 27 descends along the cam 23. The spring 26 relaxes simultaneously, and pushes the finger 19 into the slot 24: the device is armed. The user exerts a rotational movement on the branches 10 so that the large front wheel 12 comes into contact with the ground. At this time, the orifice

  18 is still not in concidence with finger 19.

  The user then transfers his weight from the seat to the back of the chair 1, which therefore tips backwards. This has the effect of raising the small front wheels 7 from the ground, and of giving the uprights 5 an inclination towards the rear. A rotational movement is then imposed on the plates 13 to

  allow the large front wheel 12 to remain in contact with the ground.

  During this rotation, the finger 19 pushed by the spring 26 slides along the inclined face 28 then, when it is opposite the orifice 18, is inserted automatically into the latter. The pivoting of the branches 10 is then locked, and the chair 1 is blocked in

the all terrain position.

  At the end of use, it suffices to unlock the chair 1 by turning the handles 15 again by a quarter turn, in the opposite direction to the first rotation. The finger 19 then turns on itself, and the stud 27 rises along the cam 23, thus pulling the finger 19 out of the orifice 18 at the same time as the spring 26 is compressed. The branches 10 are then again free to pivot, which allows the user to put the chair 1 back on the

  small front wheels 7, by tilting forwards.

  The last step is unlocking the fastening devices 16 of the boxes 14 to the uprights 5, so as to unhook the

armchair module 2.

  The above description clearly explains how

  the invention achieves the objectives it has set for itself. In particular, it offers a module for transforming a city wheelchair into an all-terrain configuration, which is easy to set up and use by the disabled person, without having to get out of the wheelchair or require the use of a

  outside help. The module according to the invention is furthermore light and compact.

  However, it follows from the above that the invention is not limited to the modes of implementation which have been specifically

  io described and represented in the figures.

  One can in particular envisage that the control boxes are formed of two separable parts, one of which remains

  permanently attached to the chassis uprights, and the other is removable and clings to the first at the time of use.

Claims (11)

  1. Wheelchair (1) essentially comprising a chassis (3) supporting a seat for a disabled person, a set of rear driving wheels (4) and a set of small front steering wheels (7) permanently mounted on uprights (5) of said chassis (3), characterized in that it comprises a removable module (2) for transforming a city armchair configuration into an all-terrain armchair configuration, comprising a large front steering wheel (12 ) disposing   along an axis of symmetry of the chair (1), mounted on a structure having branches (10) respectively connectable to said uprights (5) of said frame (3), and means placed under the control of said person to ensure the locking of said chair (1) in a so-called off-road position, reached by tilting said chair (1) rearward, and in which said chair (1) is supported only on said rear wheels (4) and on said large front steering wheel (12), said set of small front steering wheels (7) being raised enough not to come into contact with the roughness of the ground.   2. Wheelchair according to claim 1, characterized in that said branches (10) are connectable to said uprights (5) pivoting about a horizontal axis perpendicular to the direction of advance of the chair (1), and in that said module (2) comprises a locking device 25 associated with each of said branches (10), operable between a position of free pivoting of said branch (10) facilitating the installation and removal of said module (2) on said chair ( 1), and an armed position authorizing the automatic blocking of the pivoting of said branch (10) when said chair (1) reaches said all terrain position.   3. Wheelchair according to claim 2, characterized in that each of said locking devices comprises a finger (19) movable in translation parallel to the pivot axis of said branch (10), which is pushed towards said branch (10) under the action of a spring (26), and which is able to fit into a slightly larger orifice (18) arranged in said branch (10) and located opposite it when said chair (1) is in said all-terrain position, and in that said locking device comprises means for controlling the translation of said finger (19) against said spring (26), making it possible to withdraw said finger (19) from said orifice (18).   4. Wheelchair according to claim 3, characterized in that each of said fingers (19) carries a stud (27) which is perpendicular to it and which is able to move along a cam (23) arranged so that the rotation of said finger (19) on itself, under the effect of a rotational movement exerted by said person on a handle (15) integral with said finger (19), causes said finger (19) to translate perpendicular to said branch (10).   5. Wheelchair according to claim 3 or 4, characterized in that each of said orifices (18) is arranged in said branch (10) at the end of an inclined face (28) arranged so as to facilitate the pivoting of said branch (10), when said finger (19) is pushed under the action of said spring (26), until reaching the position in which said orifice (18) is located opposite said finger (19).   6. Wheelchair according to any of   claims 1 to 5, characterized in that each of said   branches (10) is connected at a rear end to a fixing device (16) respectively to one of said uprights 30 (5) of said chassis (3), said fixing device (16) being in particular constituted by a clamp capable of clamping said upright (5) over its entire circumference and provided with means for its   locking in its position enclosing said upright (5).   7. Wheelchair according to any of   claims 1 to 6, characterized in that each of said   branches (10) is connected at one front end to a steering column (11) of said large front steering wheel (12), so as to pivot around an axis parallel to said column of direction (11).   8. Wheelchair according to any of   claims 1 to 7, characterized in that said large wheel   front steering wheel (12) is of the all-terrain wheel type, preferably the same as the rear driving wheels (4), the latter being in particular each equipped with a handrail for its   manual training by said person.   9. Wheelchair according to any of   Claims 1 to 8, characterized in that said branches (10)   each extend at a rear end by a plate (13) of lesser thickness in the form of a quarter disc, which is inserted in a control box (14), by a slot (24) arranged in said box (14), and which is pivotally hinged therein about a horizontal axis perpendicular to the direction of advance of said chair (1), and in that said housing (14) comprises a device for locking the pivoting of said actuable plate (13) by said person, and a device   fixing (16) to one of said uprights (5) of said chair (1).   10. Module (2) for converting into an all-terrain configuration of a wheelchair (1) equipped in a city wheelchair configuration, characterized in that it comprises a structure having two branches (10) connected at one end to a steering column (11) of a large steering wheel (12), so as to pivot laterally about an axis parallel to said steering column (11), and each connected at another end to a fixing device ( 16) respectively to a fixed upright (5) of said chair (1), pivoting transversely about an axis perpendicular to said steering column (11), and in that said branches (10) are each associated with a device for locking of said transverse pivoting. 11. Module (2) for converting into an all-terrain configuration of a wheelchair (1) equipped in a city wheelchair configuration, characterized in that it comprises a structure having two branches (10) connected at one end to a steering column (11) of a large steering wheel (12), so as to pivot laterally about an axis parallel to said steering column (11), and each connected at another end to a fixing device (16 ) respectively to a fixed upright (5) of said chair (1), pivoting transversely about an axis perpendicular to said steering column (11), and in that said branches (10) are each associated with a device for locking of said transverse pivoting comprising a finger (19) movable in translation parallel to the pivot axis of said branch (10), which is pushed towards said branch (10) under the action of a spring (26), and which is able to fit into a slightly larger orifice (18) arranged in said branch (10) at the end of an inclined face (28) arranged so as to facilitate the pivoting of said branch (10), when said finger (19) is pushed under the action of said spring (26), until reaching the position in which said orifice (18) is located with respect to said finger (19), said finger (19) carrying a stud (27) which is attached to it perpendicular and which is able to move along a cam (23) arranged so that the rotation of said finger (19) on itself, under the effect of the rotation of a handle (15) integral with said finger (19), causes said finger to translate   (19) perpendicular to said branch (10), thus making it possible to withdraw said finger (19) from said orifice (18) against the action of said spring (26).