Abstract:
The invention described is a collapsible service trolley with left and right side compartments; one left front wall is hinged to the left side compartment; one right front wall is hinged to the right side compartment; one left back door is hinged to the left side compartment; one right back door is hinged to the right side compartment; one left upper wall hinged to the left side compartment; one right upper wall hinged to the right side compartment and hinged to the left upper wall; one left lower wall hinged to the left side compartment and one right lower wall hinged to the right side compartment and hinged to the left lower wall. In the collapsed position of the trolley each compartment contains the elements hinged thereto; in said position, the trolley is compact and easily stored.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to the techniques employed in the manufacture and design of displays and trolleys used at sites referred to as “points of sale”, including restaurants, where various products, services and food types are offered to the public; more particularly, to a collapsible service trolley. 
       BACKGROUND OF THE INVENTION 
       [0002]    In different places where the public converges for the acquisition and promotion of products and services such as exhibitions, conventions, information centers or hotels and restaurants where food and beverages are offered and carried around for tables or rooms, there exists the constant need to use service trolleys maneuvered by one person in order to swiftly carry products and food from one place to another. For instance, there exist trolleys for selling ice creams, hot-dog trolleys, dessert and beverage trolleys for use in a hotel; additionally, at supermarkets, shopping trolleys are used to carry goods and money towards the cashiers. Hence, there exists a myriad of everyday activities where service trolleys are employed. 
         [0003]    Services trolleys may include internal compartments, doors, dividing shelves and so on, whereas its manufacturing materials mainly comprise wood and metal. Nevertheless, in general terms, all these trolleys have a rigid structure and are of a bulky nature in order to carry and contain products therein in a safe manner; therefore, their main drawback is that folding or collapsing thereof is not possible when not in use, and thus be stored in a reduced space. 
         [0004]    On the other hand, there exist other types of furniture widely employed at points of sale, such as displays and counters, of which collapsible versions are available and very practical and compact sized, such as the displays by the same inventor of the present invention and disclosed in Mexican patents Nos. 212, 227; 225,710 and in the international patent application No. PCT/IB 2005/002083. However, these displays are far from meeting the purposes of service trolleys, as none includes wheels or doors to close the module base and create an internal chamber with restricted access.    
       SUMMARY OF THE INVENTION 
       [0005]    Pursuant to the above, the purpose is to eliminate the drawbacks of service trolleys known to date through the development of a sturdy and usable collapsible service trolley, with an arranged structure of its elements that allow the same to be folded into a very compact shape and stored in reduced spaces. In addition, when the trolley is in its folded position, carrying thereof is simple and swift. 
         [0006]    The collapsible service trolley of the present invention comprises one left side housing and one right side housing; both housings essentially shape the sides of the trolley. At the front part of the trolley, there is located one front left wall, which is hingedly attached to the left side housing such that it can be housed therein. In a similar fashion, there exists one front right wall hingedly attached to the right side housing such that it can be housed therein. 
         [0007]    At the rear part thereof, the service trolley of the present invention comprises one left rear door hingedly attached to the left side housing and housed therein on top of or underneath said front left wall when the latter is housed inside the left side housing. Likewise, there exists one right rear door hingedly attached to the right side housing and housed therein on top of or underneath said front right wall when the latter is also housed inside the right side housing. 
         [0008]    Now, at the upper part of the service trolley of the present invention, it comprises one upper left wall hingedly attached to the left side housing and housed therein on the rear door or the front left wall when the same are housed therein. There also exists one upper right wall hingedly attached to the right side housing and hingedly attached to the upper left wall; the upper right wall is housed within the right side housing on the rear door or the front right wall when the same are housed therein. The upper left and right walls connect said left and right side housings by their upper part. 
         [0009]    In addition, there is located one bottom left wall hingedly attached to the left side housing and housed therein on the rear door or the front left wall when the same are housed therein, and one bottom right wall is provided hingedly attached to the right side housing and hingedly attached to the bottom left wall; the bottom right wall is housed in the right side housing on the rear door or the front right wall when the same are housed therein. The bottom right and left walls connect said left and right housings by their bottom. 
         [0010]    Finally, at the bottom of the left and right side housings, wheels are mounted thereon to displace the trolley on any surface. 
         [0011]    In order to fold down the service trolley from an upright position, the front left wall is housed in the left side housing and the front right wall is housed in the right side housing; the rear left door also moves inwards of the trolley to be housed in the left side housing and the rear right door moves inwards of the trolley to be housed in the right side housing. Afterwards, the left side housing and the right side housing are brought closer to each other until they make contact, such that during this movement the upper left and right walls are folded downwardly at their attachment zone; meanwhile, the bottom left and right walls are folded upwardly on their attachment zone, and therefore said bottom and upper walls are housed in the housing on their respective side, thereby achieving the “collapsed” and compacted position of the trolley. 
         [0012]    In a first preferred embodiment of the present invention, the service trolley comprises one left shelf and one right shelf, the left shelf is hingedly attached to the front left wall and the other shelf is hingedly attached to the front right wall; each shelf runs from the front wall to which it is attached to the corresponding rear left or right door. These shelves allow the dividing of the trolley&#39;s inner space to place several items thereon. In the folded position of the service trolley, the shelves are housed inside the front wall to which they are attached. 
         [0013]    In addition, in a second preferred embodiment of the present invention, the service trolley further comprises one board and one pair of posts with upper ends onto which the board is detachably attached. One of the posts is detachably attached to the left side housing and the other post to the right side housing; the posts are made from post sections that assemble together and are stored in the trolley&#39;s side housings. With the additional inclusion of the board, the appearance of the service trolley of the present invention is further enhanced, as the same can be easily spotted by the public when said trolley is motionless or in motion at a sales point. 
         [0014]    From the above, one object of the present invention is to provide a low weight collapsible service trolley, yet sturdy and with a large volumetric capacity of its interior at the same time. 
         [0015]    Another object of the present invention is to provide a collapsible service trolley that can be easily carried around, whether in use or in its folded position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The novelty aspects deemed as unique to the present invention shall be specifically set forth in the appended claims. Nevertheless, the invention—both in terms of its structure and performance thereof—along with other objects and advantages thereof, shall be better understood with the following detailed description of two preferred embodiments, when read in conjunction with the accompanying drawings, and wherein: 
           [0017]      FIG. 1  is a left front perspective view of a collapsible service trolley built pursuant to one first embodiment of the present invention, the trolley being in its upright position. 
           [0018]      FIG. 2  is a rear left perspective view of the collapsible service trolley shown in  FIG. 1 . 
           [0019]      FIG. 3  is a rear view of the collapsible service trolley of  FIG. 1 . 
           [0020]      FIG. 4  is a rear view of the collapsible service trolley of  FIG. 1  with its rear doors opened. 
           [0021]      FIG. 5  is a rear left perspective view of the collapsible service trolley of  FIG. 1  with its rear doors opened. 
           [0022]      FIGS. 6 to 13  show the sequence of movements by means of which the service trolley of  FIG. 1  is folded. 
           [0023]      FIG. 14  shows a rear left fragmented perspective view of the service trolley of  FIG. 1 , in its folded position. 
           [0024]      FIG. 15  is front left perspective view of a second preferred embodiment of the service trolley of the invention. 
           [0025]      FIG. 16  is a front right and exploded perspective view of the embodiment of the service trolley shown in  FIG. 15 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    In reference to the accompanying drawings, more specifically to  FIGS. 1 through 4  thereof, there are shown a collapsible service trolley  1 , which is constructed according to a first preferred embodiment of the present invention for illustrative rather than limiting purposes. In the present detailed disclosure, left, right, front and rear directions of the service trolley are intended when the user is standing behind the trolley and waiting on a customer. 
         [0027]    In the collapsible service trolley  1  of this first preferred embodiment, it can be seen that there exists one left side housing  10  in the shape of a box, that is, en the shape of a parallelepiped, which essentially shapes the left side of the service trolley  1 . At the opposite side of the trolley, there is one right side housing  16  also in the shape of a box or parallelepiped. These housings  10  and  15  are hollow and have this preferred shape because in the folded position of the service trolley  1 , the remaining parts thereof shall be housed inside side housings  10  and  15 , as will be shown throughout the present disclosure. 
         [0028]    At the front part of the service trolley  1 , one front left wall  20  that is hingedly attached to the left side housing  10  such that the leg front wall  20  can be moved and housed within said left side housing  10  when the car  1  is folded. Similarly, one front right wall  25  can be seen that is hingedly attached to the right side housing  15  and housed inside the same when the car is folded. Graphic material can be placed on the surface of the front walls  20  and  25 ; also, the walls can be transparent to look inside the service trolley  1 , something useful when food is carried therein such as desserts. 
         [0029]    At the service trolley&#39;s  1  rear end one rear left door  30  can be observed that is hingedly attached to the left side housing  10  and to be housed inside the same. In the embodiment disclosed, the rear left door—when housed—remains on the front left wall  20  when the latter is also housed therein; however, in the present invention, there is no restriction on doing the opposite, that is, the front left wall  20  can remain on the rear left door  30  when housed. 
         [0030]    As can be seen as well, there exists one rear right door  35  that is hingedly attached to the right side housing  15  and to be housed inside thereof and over said front right wall  25  when the latter is housed inside the right side housing  15 . However, as in the case of the left side, there is no restriction for the front right wall  25  to remain over the rear right door  35  when housed. 
         [0031]    Now, at the upper part of the service trolley  1  of this preferred embodiment, it comprises one upper left wall  40  hingedly attached to the left side housing  10 . In the embodiment being described, said upper left wall  40  shall be housed inside the left hide housing  10  and on the rear left door  30  when the latter is housed. On the other hand, there also exists one upper right wall  45  hingedly attached to the right side housing  15  and hingedly attached to the upper left wall  40 . In this embodiment, the upper right wall  45  will be housed inside the right side housing  15  and on the rear right door  35  when the latter is housed. The upper left and right walls  40  and  45  connect said left and right side housings  10  and  15  by the upper part thereof. 
         [0032]    At the bottom of the service trolley  1 , there is one bottom left wall  50  hingedly attached to the left side housing  10  and housed therein; in the embodiment being described the bottom left wall  50  will be housed on the rear left door  30  when the latter is housed as well. The trolley  1  is also provided with one bottom right wall  55  hingedly attached to the right side housing  15  and hingedly attached to the bottom left wall  50 ; the bottom right wall  55  is housed inside the right side housing  15  and on the rear right door  35  when the latter is also housed in the right side housing. The bottom left and right walls  40  and  45  connect said left and right side housings  10  and  15  by their bottom. 
         [0033]    The service trolley  1  includes wheels  2  that are assembled to the bottom of the left and right side housings  10  and  15 , the wheels allowing movement of the trolley on any surface. In particular, the wheels  2  are arranged in two pairs, one of these pairs of wheels  2  is assembled at the bottom of the left side housing  10  and can be rotated so that the trolley is guided towards the left or right when it is driven. Meanwhile, the other pair of wheels  2  is assembled to the bottom of thee right side housing  15  and only pivots over its horizontal axis. As can be seen particularly in  FIGS. 3 and 4 , the size of the left side housing  10  than that of the right side housing  15 , mainly due to the assembling of the wheels on the left side housing  10  that allows the trolley to be turned; however, there is no restriction in the sense that both side housings  10  and  15  are sized the same and that the pairs of wheels pivot over one vertical axis or not. 
         [0034]    Driving of the service trolley  1  takes place by pushing the trolley  1  by means of the driving bar  3  which is mounted as shown on the upper and lateral part of the right side housing  15 , although there are no restrictions as well for the driving bar  3  to be assembled to the left side housing  10  or that a second driving bar is simultaneously included at the left side housing  10 . 
         [0035]    Reference is now made to  FIGS. 4 and 5  that show two rear views of the service trolley, with their rear doors  30  and  35  open to show the interior of the service trolley  1 . In particular,  FIG. 4  shows the rear face of the front walls  20  and  15 , respectively from which one left shelf  60  and one right shelf  65 ; the left shelf  60  is hingedly attached to the front left wall  20  and the right shelf  65  is hingedly attached to the front right wall  25 . In the service trolley  1  upright position, each shelf  60  and  65  run from the front wall to which it is attached towards the corresponding rear left  30  or right  35  doors. In addition, each shelf  60  and  65  is attached to the corresponding rear door by first fixing means that, in the embodiment being disclosed, correspond to the bases or pinned brackets  61  and  66  that are mounted at the door frames  31  and  36  that are part of the corresponding rear left and right doors  30  and  35 . 
         [0036]    It is important to point out that these left and right shelves  60  and  65  are an option, but in the embodiment described, serve to split the inner space of the service trolley  1  and arrange the items being carried in the trolley. In the folded position of the service trolley  1 , each left and right shelf  60  and  65  are movable and can be fixed in a vertical position to the front wall to which it is attached. For this purpose, second fixing means are used that, in the embodiment being disclosed, belong to the Velcro® co-operating portions  62  and  67  (hook and fiber fixing portions) provided both at the rear face of the front walls  20  and  25  and at the upper face of the shelves  60  and  65 . In the embodiment being disclosed, the shelves  60  and  65  move upwardly so that the Velcro® portions  62  (hook and fiber fixing portions) on the left side hook between each other, and the same can happen with the Velcro® portions  67  (hook and fiber fixing portions) on the right side. In the same regard, there are no restrictions for the shelves  60  and  65  to be moved downwardly and secured over the upper wall to which they are attached if hook and fiber fixing portions (Velcro®) are provided at the bottom of the front walls and at the bottom face of the shelves  60  and  65 . Furthermore, there are no restrictions regarding the use of other fixing means such as clasps, male-female couplings that allow the shelves  60  and  65  to be fixed in a vertical position to the front wall  20  or  25  to which they are attached. Each shelf  60  and  65  is preferably manufactured of a single PVC plate whose ends are bent with heat in order to form rounded edges, although they can also be made from a plate supported on a frame that is hingedly attached to the corresponding front wall  20  or  25 . 
         [0037]    Still in reference to  FIGS. 4 and 5 , it can be mentioned that the rear right door  35 , in addition to its door frame  36 , includes one inner frame  37  that provides stiffness to the rear right door  35  and one plate  38  that is attached on top of said inner frame  37 . The plate  38  is hingedly mounted to the door frame  36  by means of the hinge  39  to allow opening and closing of the rear right door  35 , thereby to gain access towards the interior of the service trolley  1  (see  FIG. 5  in particular). 
         [0038]    Now, in order to allow the rear right door  35  to be housed inside the right side housing  15 , the door frame  36  is hingedly attached by the right side thereof to the internal surface of said right side housing  15 ; in other words, the right side of the door frame  36  is attached inside the right side housing  15 . Accordingly, when the rear right door  35  is secured to its door frame  36 , the entire door  35  moves towards the interior of the service trolley  1  so that the rear right door  35  is housed in the right side housing  15 . In  FIG. 4 , the right side of the door frame  36  is represented by a broken line as it is hidden by the right side housing  15 . 
         [0039]    On the left side of the service trolley  1 , the same structural relationship of the rear left door  30  with the side housing  10  exists on the same side; i.e., in addition to the door frame  31 , the rear left door  30  is formed by the inner frame  32  and the plate attached on top of said frame to cover the same, the plate  33  is hingedly attached to door frame  31  so that the rear left door  30  can be opened and closed over its door frame  31 . Meanwhile, the door frame  31  is hingedly attached by its left side to the internal surface of the left side housing  10  so that the entire rear left door  30 —including its frame  31 —can be housed inside the housing  10  from that same side. In  FIGS. 4 and 5 , the left side of the door frame  31  is represented by a broken line for clarification purposes and for showing that it is attached to the left side housing by its interior. 
         [0040]    The rear left and right doors  30  and  35  include first locking means to block the door to its corresponding door frame  31  and  36 , these means are the locks  4  that can also be seen in  FIGS. 2 and 3 . Likewise, padlocks can be used as the first locking means. 
         [0041]    Reference is now made to  FIGS. 6 through 13  to disclose the manner in which the car is being folded. In order to avoid confusion regarding the number references in such  FIGS. 6 and 13 , only the elements that move to allow the folding of the service trolley  1  are shown. 
         [0042]    To start with, in  FIGS. 6 and 6A  the right shelf  65  of the service trolley  1  is released from the base pinned base  66  with an upwardly movement; it should not be forgotten that the pinned base  66  is mounted to the door frame  36  of the rear right door  35 , the base  66  serves to fix the shelf  65  in a horizontal position when the trolley is in a upright position. With special reference to  FIG. 6A , which shows how the right shelf  65  stands up to be released from the base  66  and vertically fixed on the internal face if the front right wall  25  by means of the Velcro® co-operating portions  67  (hook and fiber fixing portions). In the embodiment shown, the front right wall  25  is formed of one frame  26  and one plate  27  that is attached to and covers said frame. In order to allow the right shelf  65  to hingedly attach to the front right wall  25 , one shaft  68  is mounted on the internal face of the frame  26  and received inside the right shelf  65 . 
         [0043]    Although not shown in  FIGS. 6 and 6A , it can be mentioned that on the left side of the service trolley  1 , the left shelf is risen to be housed inside the front left wall, and so the service trolley reaches a position where both left and right shelves  60  and  65  are secured in a vertical position to the corresponding front left and right wall  20  and  25  as shown in  FIG. 7 . 
         [0044]    From  FIG. 7 , it can be mentioned that while the trolley  1  is in its upright position, said front left and right walls  20  and  25  are interconnected to each other to provide structural stiffness to the front part of the service trolley  1 . The front left wall  20  is formed of one frame  21  and one plate  22  attached thereon and, as mentioned, the front right wall  25  is formed of the frame  26  and the plate  27 . For interconnection between both front walls  20  and  25 , first connection means are used that, in the embodiment being shown, comprise one pair of sliding pins  23  that may be provided inside the frame of the front left or right wall. When laterally slid, each pin is inserted in the frame of the opposite front wall, so as to interconnect both front walls. 
         [0045]    In  FIG. 7 , it can be seen that the pins  23  are provided inside the frame  21  of the front left wall  20 , specifically one of these pins is provided inside the bottom side of the frame  21  and seen in detail “A” of  FIG. 7 , the other pin being provided in the upper side of the frame  21  of the front left wall  20  and not perceived in  FIG. 7 . Detail “A” shows that the pin  23 , when laterally slid it is inserted inside the frame  26  of the front right wall  25 . More specifically, the pin  23  consists of one hollow tubular profiles portion that runs inside and laterally within the frame  21  of the front left wall  20 . The pin is driven by means of the head bolt  24  and runs alongside one channel  28  provided on the frame  21  of the front left wall  20 . Other means to interconnect the front walls  20  and  25  can also be provided such external hooks or pins. Nevertheless, the hooks are the best fit for the embodiment being disclosed, as they are essentially hidden. 
         [0046]    In order to house the front walls  20  and  25 , the same have to be disconnected by removing the pins from the frame  26  of the front right wall, and as a result the front left and right walls  20  and  25  become disconnected and move towards the side housing  10  or  15  to which they are attached in order to be housed inside the same, as shown in  FIG. 8 . Furthermore, in order to allow the front left and right walls  20  and  25  to remain fixed inside the housing by their corresponding side, the frame  21  from the front left wall  20  and the left side housing  10  are provided with third fixing means as the Velcro® co-operating portions  11  (hook and fiber fixing means) that hook between each other (see FIG.  7 ). Similarly, in the frame  26  from the front right wall  25  and inside the right side housing  15  there are also provided Velcro® co-operating portions  16  (hook and fiber fixing means). Other means to fix the front left and right walls  20  and  25  inside their corresponding housing can also be employer, however, the Velcro® portions  11  and  16  (hook and fiber fixing means) can be easily adhered to the corresponding surface and are barely perceptible, and therefore are preferably employed for such purpose. 
         [0047]    Reference is now made to  FIGS. 9 and 10 , in order to describe the manner in which the rear left and right doors  30  and  35  are housed inside the corresponding left and right housings  10  and  15  of the service trolley. For this purpose, both doors  30  and  35  move towards the side housing  10  and  15  to which its door frame  31  and  36  is attached. When housed, the rear doors  30  and  35  remain on the front wall of the corresponding side where these doors had already been housed into, as described before. Again, there is no restriction for the rear doors  30  and  35  to be housed inside their corresponding housing before the front walls  20  and  25 . 
         [0048]    Specifically,  FIG. 11  shows a top plan view of the collapsible service trolley  1  according to the position reached in  FIG. 10 . It is convenient to point out that the rear left door  30  is represented in broken lines in  FIG. 11 , said door being housed inside the left side housing  10  and on the front left wall  20  that had previously been housed. In the same manner, the rear right door  35  is shown inside the right side housing  15  and on the front right wall that had already been housed. Likewise, the hinge  34  is shown by means of which rear left door  30  is hingedly attached to the left side housing  10 , as well as the hinge  12  by means of which the front left wall  20  is attached to the left housing  10 . On the right side of the trolley there is shown the hinge  39  that allows the attachment of the rear right door  35  to the right side housing  15  and, finally, there is shown the hinge  29  that allows the attachment of the front right wall  25  to the interior of the right side housing  15 . 
         [0049]    Still in reference to  FIG. 11 , it should be mentioned that the upper left wall  40  is formed of one frame  41  on top of which one plate  42  is attached, the upper left wall  40  is hingedly attached to left side housing  10  by means of the hinge  43 —shown in broken lines—as it is internally adhered to the left side housing  10  and to the left side of the frame  41 . On the other hand, the upper right wall  45  is formed of one frame  46  on top of which one plate  47  is attached. The upper right wall  45  is hingedly attached to the right side housing  15  by means of the hinge  48  that is internally attached to the right side housing  15  and to the right side of the frame  46  of the upper right wall  45 , which in turn is hingedly attached to the upper left wall  40  by means of the hinge  49 . 
         [0050]    Now, as mentioned before, in the service trolley  1  upright position, the upper and right walls  40  and  45  are interconnected between each other by second connection means to provide structural stiffness to the upper part of the service trolley. In the embodiment disclosed, said second connection means are one pair of pins  44  that provided inside of the front side and the upper side of the frame, whether from the upper left or right wall, each pin when laterally slid is inserted inside the frame of the opposite upper wall to interconnect said upper walls  40  and  45 . 
         [0051]    More specifically, the pins  44  are provided inside the frame  46  of the upper right wall  45 , each pin  44  when laterally slid is inserted inside the frame  41  of the upper left wall  40  to connect said upper walls  40  and  45 . Furthermore, the pins  44  consist of one tubular profile portion that runs internally and laterally within the frame  46  of the upper right wall  45 . Each pin  44  is driven by the head bolt  18  that runs alongside the channels formed in the frame  46  of the upper right wall  45 . As shown in  FIG. 11 , the pins  44  have a similar structure and function to that of the pins  23  shown on detail “A” of  FIG. 7 . 
         [0052]    As a previous step to the housing of upper walls  40  and  45 , the latter have to be disconnected by removing the pins  44  from the frame  41  of the upper left wall, with which the upper left and right walls  40  and  45  become disconnected but remain together with the help from the hinge  49 . 
         [0053]    Now, reference is made to  FIG. 12  that shows a bottom plan view of the service trolley  1 . From this figure, it is perceived that the bottom left and right walls  50  and  55  have a similar structural relationship to that of the upper left and right walls. More particularly, the bottom left wall  50  is formed of one frame  51  on top of which one plate  52  is attached, the upper left wall  50  is hingedly attached to the left side housing  10  by means of the hinge  53 —shown in broken lines—as it is internally adhered to the left side housing  10  and to the left side of the frame  51 . On the other hand, the bottom right wall  55  is formed of one frame  56  on top of which one plate  57  is attached. In addition, bottom right wall  55  is hingedly attached to the right side housing  15  by means of the hinge  58  that is shown in broken lines. The bottom right wall  55  is also hingedly attached to the bottom left wall  50  by means of the hinge  59 . 
         [0054]    Likewise, regarding the upper walls in the upright position of the service trolley  1 , the bottom left and right walls  50  and  55  are interconnected between themselves by third connection means, which in the embodiment described are one pair of sliding pins  54 , which are provided inside of the front side and rear side of the frame of the bottom left or right wall; when laterally slid, each pin is inserted within the frame of the opposite bottom wall so as to connect both bottom walls. 
         [0055]    Specifically, pins  54  are provided inside of the frame  56  of the bottom right wall  55 ; specifically one pin  54  is provided in the front side and the other one in the rear side of said frame  56 . When each pin  54  is laterally slid, it inserts itself in the frame  51  of the bottom left wall  50  in order to interconnect said bottom walls  50  and  55 . More specifically, the pins  54  consist of one tubular profile portion that goes inwards and laterally inside the frame  56  of the bottom right wall  55 . Each pin  54  is driven by the head bolt  19  that runs along the channels provided in the frame  56  of the bottom right wall  55 . 
         [0056]    As a previous step for housing the bottom walls  50  and  55 , the inner pins  54  have to be removed from the frame  51  of the bottom left wall  50 , thereby the bottom left and right walls  50  and  55  are disconnected, but they remain attached due to the hinge  59 . On the other hand, the wheels  2  and the driving bar  3  previously described in  FIG. 12  can be clearly seen. 
         [0057]    Once the upper walls  40  and  45 , as well as the bottom ones  50  and  55  have been disconnected when the pins  44  and  44  shown in  FIGS. 11 and 12  are released, the only thing to do is to bring the left and right side housings  10  and  15  closer as shown in  FIG. 13  until the housings make contact by this movement. During this action, the upper left and right walls  40  and  45  fold downwardly in their attachment zone, i.e. over the hinge  49 ; meanwhile, the bottom left and right walls  50  and  55  fold upwardly over their attachment zone which is the hinge  59 , leaving said bottom and upper walls housed in the respective side housing, thereby achieving the trolley&#39;s “folded down” position, which is very compact as can be seen in  FIG. 14 . This bringing closer between the housings  10  and  15  is provided by the wheels  2  on top of which said housings move. 
         [0058]    To prevent that the service trolley  1  lose its folded position, second locking means are provided which are included in the front and rear sides of the housings  10  and  15 ; in a preferred way, said second locking means are locks or padlocks  5 . 
         [0059]    In  FIG. 14  that shows the folded position of the service trolley, it can be seen that the front left wall  20 , the rear left door  30 , the upper left wall  40  and the bottom left door  50  are housed in the left side housing  10 . Meanwhile, in the right side housing  15 , the front right wall  25 , the rear right door  35 , the upper right wall  45 , and the bottom right wall  55  are housed. In the folded position shown in  FIG. 14 , the service trolley  1  can be tilted in order to be pulled by the driving bar  3 . 
         [0060]    In order to show the compact shape that the service trolley  1  can achieve and without being a limitation for the present invention, the service trolley  1  in its folded position has a characteristic length of  16  cm from one housing to another, whereas in its upright position, it has a length of about 76 cm.; i.e., in the folded position of the trolley, the length is reduced by about 80% versus the upright position thereof. Height and width of the trolley are about 84.5 cm. and 40 cm. respectively. 
         [0061]    Now, reference is made to  FIGS. 15 and 16  that show a second embodiment of the service trolley of this invention; this second embodiment is identified by number  1 ′. As readily seen, the service trolley  1 ′ of this second embodiment has, as additional elements, one board  70  and one pair of posts  71 , to which upper end said board  70  is removably attached. Besides, one of the posts is removably attached to the left side housing  10  and the other post  70  is attached to the right side housing. To do this, the posts  71  are inserted in cavities  17  which are included at the upper part of the right and left side housings  10  and  15  (see detail “D” of  FIG. 16 ). The board is formed by one sheet  74  attached over mounting bases  75  that are in the upper part of the sheet  74 . 
         [0062]    The posts  71  are formed by post sections that assemble between each other; particularly, they are formed of one upper section  72  and one bottom section  73 . In particular, the bottom end of the upper section  72  is inserted in the upper end of the bottom section  73 , see detail “C” in  FIG. 16 . In order to assemble the board  70  to the posts  71 , the mounting bases  75  fit together to the upper end of the posts  71  (See detail “B” of  FIG. 16 ). 
         [0063]    One important issue is that the post sections  72  and  73  can be housed within the side housings  10  and  15 , particularly by the corners thereof. Meanwhile, the board  70  can be housed in one of the housings as well, preferably inside the right side housing  15  that has a greater height regarding the left housing  10 . With the inclusion of the board  70 , the service trolley  1 ′ of this second embodiment can be easily placed at any point of sale. The remaining elements  2 ,  3 ,  20 ,  25 ,  40 , and  45  of  FIGS. 15 and 16  are the wheels, the driving bar, the front left and right walls and the upper left and right walls respectively, which already have been described for the first embodiment and that do not change for the second embodiment of  FIGS. 15 and 16 . 
         [0064]    The service trolley of the present invention, in any of its embodiments, is highly resistant and it is preferably manufactured in polymeric materials such as PVC. More specifically, the post sections, wall frames and the doors are manufactured with extruded PVC profiles. The hinges employed are plastic hinges that adhere to the plates or to the frames with no need to bore as would be needed when metal hinges are used; however, there is no restrictions as to the use of this or other kind of hinges. On the other hand, the plates of the shelves, as well as the left and right side housings are manufactured in foamed PVC. Metal parts are limited except for the locks  4  and  5 . The inner volume of the service trolley in its upright position is about 0.25 m 3 , without implying a size restriction, as it can be seen that with the principles of the present invention, trolleys of greater or lower capacity can be built. 
         [0065]    As shown, the structural relationship among the elements of the collapsible service trolley allows its storage in a compact way; nevertheless, it is very resistant and can be used in countless applications as disclosed in the background of this disclosure. 
         [0066]    Although the preferred embodiments of the present invention have been described, it should be emphasized that numerous modifications thereof are possible; e.g., the front walls can be housed over the rear doors, the type of hinges used, manufacturing materials, etc. Therefore, the present invention shall not be deemed as restricted except for the teachings of the prior art and by the scope of the appended claims.